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“I was just asked to balance a Binary Search Tree by JFK's airport immigration” (twitter.com)
660 points by z3t1 on Feb 27, 2017 | hide | past | web | favorite | 314 comments

Once (also in JFK) I was quizzed a bit by the CBP officer. I told him I was a math grad student, he said "well, then tell me about the Euler problem". I explained that Euler was a fairly prolific guy, and asked if he could be more specific. He didn't relent, apparently he had seen some documentary that was all about the "Euler problem".

Eventually, we moved on to my background, and I mentioned I had done a masters in computational neuroscience. He said something like "oh neuroscience, my great aunt had that", I think he thought it was an illness? Was sort of expecting the reality TV cameras to be busted out at that point...

He let me through though! Usually I clear immigration in Ireland (one of the few places you can do the immigration before you leave), and those folks are always much more pleasant.

I was going to SV and landed at SFO. The flight was long and I was tired, and raised additional suspicion of the security guy. He asked me about the purpose of my (two-week-long) visit. I replied "software integration". He asked then, "what sort of software integration can be done in only 2 weeks?" I must say, this question remained unanswered. He let me in, it was 2006.

"None, but don't tell management that please."

I would advise strongly against that kind of snarky or funny responses. It is a no-no. Give a standard answers the lawyer might have presented you.

I dunno, when I was coming back from Europe a while back the homeland security guy in the airport asked me if I wanted a full cavity search. I was like "no?..." And he was like, ah, you don't fit the profile anyways.

I've found American Border Patrol and Customs to be fairly relaxed though. I am a white American guy from the Midwest, so that may have something to do with it. I find the TSA to be more of a pain.

The real problem with border patrol is that how you are treated depends entirely on the individual border agent. I've had agents joke with me, I've had agents grill me. I've even had an agent with an earphone in his ear, dance music pumping, as he stamped my passport and visa in time with the beat.

I've long since learned the lesson that joking around with them is absolutely never, ever worth it. It's sad, because it presumably makes their jobs joyless, and the actual nice people more likely to leave. But here we are.

> But here we are.

The terrorists are winning. sigh

“No” (in a different tone perhaps) or “no thanks” does seem like the straightforward, serious answer to that question.

Maybe Hollywood should make a "Party Patrol" about a group of CBP officers joking with hungover college kids returning from spring break in Mexico. Think along the lines of "Super Troopers".

Oh if you are American and/or white it is a different case.

I know, all these European migrants are running around out here scared because Lord Merkel tells them to be when they have nothing to worry about

Its a hard point to convey without really spelling out the underbelly of American society

If anything it's Granny Merkel and we don't need her to be worried. What really scares me is that people seem to believe anything they read/heard/watched on the internet without checking or even asking for the source of the claims/news. O, and Trump scares me. Not because I fear a war or something. But because he's a negative example of the good old 'anything is possible in America' and he somehow deleted that 'land of the free' part...at least in my version of reality (yep, that's ok, everybody got his own reality. But we're all in IT here, we know that, right?

> asked me if I wanted a full cavity search

If you wanted?!

No way this is real.

Threats are common. I was flying within the USA with a young toddler still nursing. We had some breast milk and was ordered to dump it, by a TSA agent, standing in front of a sign saying milk was fine.

I mentioned the sign and was threatened with a "deep" inspection and guaranteed enough detention time to miss the flight.

We dumped it, boarded a 5 hour flight, pushed the call button and asked for cow milk to help get through the flight. They came back, 3 other moms did the exact same thing, and got told they were out of milk.

Quite unpleasant, security theater is such a waste.

I was once traveling back from Italy after attending PKDD conference. I was really sick and had a really bad headache, so the following exchange really scared me:

    "Why did you go to Italy?"
    - To attend a conference.
    "Which conference did you attend?"
    - European Conference on Machine Learning
    "Machine Learning? (smile) How do you learn from machines?"
I forgot the exact answer I gave, but I was pretty afraid that he had a Wikipedia page on "Learning from Machines" and would not let me pass if I failed.

I imagine their main goal is to keep you talking. More questions they ask, the more you need to answer and the more they can watch your body language and responses for signals.

And completely misinterpret it: http://www.nature.com/news/2010/100526/full/465412a.html

"Yet a growing number of researchers are dubious — not just about the projects themselves, but about the science on which they are based. "Simply put, people (including professional lie-catchers with extensive experience of assessing veracity) would achieve similar hit rates if they flipped a coin," noted a 2007 report1 from a committee of credibility-assessment experts who reviewed research on portal screening.

"No scientific evidence exists to support the detection or inference of future behaviour, including intent," declares a 2008 report prepared by the JASON defence advisory group. And the TSA had no business deploying SPOT across the nation's airports "without first validating the scientific basis for identifying suspicious passengers in an airport environment", stated a two-year review of the programme released on 20 May by the Government Accountability Office (GAO), the investigative arm of the US Congress."

Are you sure he wasn't just joking around? I've had a TSA officer joke around asking me if I hacked into their devices (I was wearing a hackathon t-shirt)

> Are you sure he wasn't just joking around?

One rule of thumb is that you Never joke with the airport security (1). So wouldn't that go both ways?

1) https://www.theguardian.com/commentisfree/oliver-burkemans-b...

So you're saying I should better not sport my new t-shirt in the airport?


My then-teenage brother once went through US immigration wearing a t-shirt branded with the initials of the then-popular brand, French Connection UK.

Needless to say the US immigration officials took some offense and asked him a bunch of questions. I'm not sure they realised it didn't say what they thought it did, even after we explained about French Connection.

These were obviously simpler times as I also as a teenager once went through US immigration wearing a Threadless Community Party t-shirt: https://www.threadless.com/product/383/the_communist_party

The dyslectic f*ck brand was and still is annoying. In Melbourne AU they had a 20 or 30 metre tall logo covering an entire wall of an industrial building. Very glad to see it gone.

A friend of mine got pulled aside for extra questioning at Newark in the mid-90s because he was wearing a t-shirt that proclaimed "Smoke me a kipper, I'll be back for breakfast". I think the officer presumed it was some sort of drug reference.

What a guy.

I'm not going to tell you what you can and can't do. But a quick google should show you how wise that is. Or rather, isn't:


RIP the First Amendment.

Probably don't wear a shirt with blinking lights on it either.


In what possible universe do you think that TSA/border security/etc. is a power-symmetric universe? Of course they'll joke around and abuse their power if they like it - you, me and everyone else they're inspecting are powerless to them and they'll happily use that fact.

I wouldn't say never, but you need to let them initiate it and it needs to be obvious. I've had them bust my chops before - some are funny people, and others are looking to seeing if you're too tense or acting odd.

I've noticed lately that there are now TSA agents in the security lines which are ostensibly there to help direct people, but you can tell they are very high social aptitude people and very smooth. They are feeling people out and seeing if anyone is super nervous or suspicious.

I noticed this before they instituted the "random arrow iPad." I'm not sure about their level of social aptitude though. I got sent to the quick screening line 5 or 6 times in a row, but the people I saw flagged for the slower screening were people who I thought looked calm but less whitebread than me. People with their hair dyed blue, holes in the knees, etc.

I think the person who is actually reading people is the person who checks your ID and boarding pass. Though honestly I think that process would be pretty easy to fool either way.

I agree with you in general, but it's important to keep in mind that border patrol and airport security are two almost completely unrelated things.

You don't, but there are jokes and jokes (and they certainly do joke sometimes)

From stories I heard airport security is more serious than CBP though

A couple of times I've managed to defuse TSA officers after they're convinced I'm not a danger to the country, and they turn into humans again. Once I was visiting just to meet a friend and we were planning on a road-trip up to Canada. The officer quizzed if we were going in order to do drugs (which is a thing apparently?), and when I answered in the negative he sighed, said "ah, I was young once too" and let me in...

I was there to do some training, to teach the guys there how to use Yocto, Qt, etc., and the officer asked me: "So you're coming in to teach us so we can take your job?" Needless to say that I was really confused.

Could be :) Unfortunately I was feeling really bad that day so I was a little paranoid.

I'm glad I don't work at Wikipedia, because after what happened to that guy I'd be tempted to detect if a request comes from any TSA terminal and serve midget porn instead :)

One time, while going into Panama, the border agent wrote a couple words on a sheet of paper and asked me to pronounce them: ship, sheep. Thinking this was some kind of shibboleth, I complied. She then wrote a couple more, I think they were chair and share, again I complied. Finally she wrote another pair, I don't remember what exactly, but I was getting very worried that this was some kind of bizarre profiling by accent and I was about to find myself in a Panamanian detention center.

She looked up and laughed, and in very broken English explained she was trying to use the accents of incoming Americans to improve her accent to help in her job when dealing with English speaking foreigners.

As an additional data point, in 2000, both a fellow traveler and I were asked mathematical questions by US immigration officers in Canada. He answered correctly, I was unable to do so, but we were both allowed to enter without further investigation. I thought the experience was fine.

I have had less pleasant, aggressive questioning dealing with British immigration when flying into Heathrow as well as Irish immigration when flying out of Heathrow, though in the latter case the proximal cause was my fellow traveler choosing to lie. :(

> He answered correctly, I was unable to do so, but we were both allowed to enter without further investigation.

It's like that cliché often employed in coding interviews, but immigration officers are more serious about it: They don't need a correct answer, they are interested primarily in observing your answering process.

It may be a bit dated nowadays, but from travelling through Central America back in the 80s, I made it a habit to never ever use the phrase "fellow traveler" around US border officials:


Thanks for the reference! I didn't know about that euphemism.

Ah, the good old prisoner's dilemma.

> Usually I clear immigration in Ireland (one of the few places you can do the immigration before you leave), and those folks are always much more pleasant.

FYI: It's not just Ireland that let's you clear US-immigration before departure: https://en.wikipedia.org/wiki/United_States_border_precleara...

I've been going through Dublin myself for years, and I can highly recommend it: In worst case, you'll be told to leave the terminal, but you won't go into a holding cell - and yes, officers there are much more friendly than their counterparts in the US (I guess they are all infected by the Irish hospitality).

I've got some bad news for you, there's a bill being debated in Canada about giving US officials the discretion to hold or detain travellers at pre-clearance centres:



If it passes in Canada, it's only a matter of time before it happens in Ireland (or you lose the pre-clearance option).

I entered the US a few times on a visa waiver for business, and (truthfully) stated my business as "teaching dating advice to men". I got a lot of laughs, but luckily no actual in-depth questions.

He probably meant the problem of the seven bridges of Koenigsberg, which was solved by Euler, and is one of the easiest to explain to laypeople, which is good for making documentaries.

I'm not saying we shouldn't resist these types of arbitrary unofficial screening processes whenever we encounter them but if I weren't such a confrontational type of person for these things, I would just listen to my lawyers and just bring employment verification letter and visa letters with me whenever I travel abroad.

Most of Canada has USA immigration in their airports, so it's not exactly rare.

Canada, Ireland, and Abu Dhabi do US immigration at their own airports before you leave. I've never heard of any other pair of countries with any similar arrangements.

Indeed Canada, Ireland, and Abu Dhabi wait until you arrive there from the USA to do their own immigration so it only goes one way.

US preclearance exists in certain airports in Canada, Ireland, Bermuda, the Bahamas, Aruba, and the UAE.

The US-Canada agreement is the oldest one, largely due to the amount of cross-border air travel, and Canada has the right under the agreement to operate preclearance stations for the Canadian border inside US airports, but has never chosen to do so.

I've learned that, when coming to the US from Europe, if I can't get a direct flight, I prefer my change to be in Canada. This way, I can pass immigration on the Canadian airport, while I'm idling between flights anyway. Also, the one time I did it, there was almost no queue (in Toronto).

When I had a connection in Canada, my incoming flight was delayed, the lines were long and I was at risk of missing my connection, so I made the opposite conclusion.

France and UK when traveling by train.

Finland to Russia on train, the Russian Border security checks you while the train is still in Finland, speeding 200km/h towards Russia. And vice versa when going in the other direction.

Saves a lot of time and hassle.

That's awesome. Did the crossing a couple of decades ago and that was also the case, though not when 'speeding' but when changing engine at the border, and then it didn't go 200km/h at any point, and that's probably a good thing as there were man-sized gaps between left and right of the iron floating bridge connectors between carriages, but same principle.

Every long distance international train ride I've done has involved handing the conductor your passport if on a sleeper (typically overnight crossing), or someone coming round to check if it's not a sleeper.

Also from Switzerland to France, if departing from Geneva. As well as Geneva airport having a dedicated section for flying to france.

The same practice was recently implemented for a train from Ukraine to Poland.

Same when travelling by ferry across the Channel.

And ferry.

Not sure if Abu Dhabi still does it. It has, however, been an unmitigated disaster:


In case anyone is looking for some alt-anecdata on that: I was surprised to see that article, because I've been through that facility 4 times and every time has been excellent and fast (I'd even say faster than my experience in Dublin, though that was fine too). I much prefer it than having to do it after landing after 30 hours of flying... ymmv i guess

Maybe you where flying at different times? I can imagine that when they fill up four wide bodies within a couple of hours that this can be problematic.

What sounds really, really annoying is that there are no facilities whatsoever (save for a coffee kiosk) and that you can't even sit down until the gate opens.

Personally, I wouldn't know since I never flew via Abu Dhabi (let alone to the US).

Etihad are still advertising it on their flights. The entire airport is a bit of a disaster to be honest.

Sweden just got a deal for the same arrangement with the US.

That's crazy dangerous considering the recent terrorist incidents

Yeah, Tim Pool just finished his visit to Sweden. He barely made it out alive

(he ate too much dangerously delicious lasagna when in Malmo)

Haha! Can not tell if serious... :-/

Don't worry. Sweden will rebuild. #SwedenIncident


And Manchester will be the first UK airport with preclearance.

Driving the Channel tunnel between UK and France, they each have "immigration" on the opposite sides. You drive through the French passport control before you get into the tunnel to leave the UK.


There's a tunnel that goes under the channel connecting the two countries.

It's a train tunnel though, so you cannot technically drive a car there.

Well you drive onto the train and you stay in your car and drive out. So yeah, you do drive a car there, the ground beneath you changes but you haven't really stopped driving.

Israel in Greece

And in Geneva airport

Exiting Germany to fly to UK we do get checked. UK does not do an exit check when flying back the other way.

Ya, sure it's one way. I'm not sure how my comment was interpreted as meaning anything else.

I wonder if P = NP would end up being proven by someone who didn't want to be sent back after 23 hours of traveling.

I can see it now. In 100 years we will learn about how a TSA clerk who had failed mathematics back in grade school went on to prove P = NP and become synonymous with "genius" for generations.

I think he meant by a traveler who is stopped by a TSA agent.

Sure, but they gave the TSA Agent a copy of their proof...

No no no! Why did you have to do that? Don't you know they scan HN for easy to memorize one-liner questions to add to their question bank? Now those who enter the US are really doomed! :-)

I hope not, or the TSA will show off how The Question is useful for the nation's science.

More I read about things like these, even more I love Germany (my new home). The officers in Frankfurt Airport are always nice and I never had any problems nor heard about one. I hear it's even better in Berlin.

I don't understand why host countries don't try to make themselves the most favorite country in the world for their guests. I believe, "not allowing terrorists/drug dealers/illegal workers etc. etc. inside" is just the marketing as I seriously doubt people who slip through the cracks of a saner screening process would be a significant problem. Therefore, I wonder the real reason but can't think of any.

> Therefore, I wonder the real reason but can't think of any.

You shouldn't think of governments as agents with a singular, unified purpose. What you're observing is the effect of many agents with misaligned incentives, and a huge coordination problem. All this leads to a situation where large costs are incurred for no real purpose, because no agent is incentivised to put what you called 'marketing' in doubt.

For example, it's a huge cost for a politician to argue that fear of terrorism is overblown. So pretty much none of them do that. TSA have no incentive to reduce their powers. Etc.

> "not allowing terrorists/drug dealers/illegal workers etc. etc. inside"

All three of those have an access to a very sophisticated immigration scam operatives. Terrorist get extensive training in faking their identities, drug dealers have huge network of contacts and insider moles and illegal workers know the trafficking cartels.

The real reason of American immigration fiasco is deep rooted racism and against primarily non-white people. You will barely hear anything from any politicians about white people who illegally come and stay in USA from Canada and Europe. If H1B beneficiaries were mostly British or Canadians US government would have increased the limit 5x by now.

> All three of those have an access to a very sophisticated immigration scam operatives.

While that is true in many cases, in many others it is not. I lived on a border town for a few years and made friends with some DHS agents there. Listening to their stories re drug trade I got the impression that many of the people carrying drugs over are actually poor, uneducated, uninformed, etc. While some of the techniques may be sophisticated, I got the impression that the traffickers themselves frequently were not. I would imagine basic abrasive interrogation techniques would be reasonably effective.

Devil's advocate -- maybe the poorly educated, poorly trained traffickers were overrepresented in the sample of traffickers border agents encountered, because, by definition, a successful trafficker is not caught or observed trafficking.

I flew to eastern Europe three years ago and had a stop-over in Tegel both ways. It was like traveling in the US before 9/11. I felt like a human being whose rights were self-evident. It was civil. I felt human. I also felt ashamed of the industry my country has built out of fear.

Try flying to Europe from an eastern bloc country, see if you feel civil then.

In America we take our prosperity for granted. We assume we will always be rich and don't need to compete for tourism, open business and trade, general reputation etc, especially with "foreigners."

Same here, I love Germany! <3

Germany loves you, too

In a away this actually makes sense. Instead of relying on automatic systems and algorithms, you rely on people, namely the agent performing the interview. A short chat about selected topics might be actually quite revealing. Point not being if you know the exact right answer for the BST question but more how you react and if there are inconsistencies in your story (most people are pretty bad at lying).

All of this could be backed by the personal data has been collected before hand.

The old (and often linked?) article about airport security in Israel[1] describes how the actually rely a lot on people being able to spot strange behavior.

[1] http://www.huffingtonpost.com/daniel-wagner/what-israeli-air...

What would happen when I answer with "I don't know what a Binary Search Tree is or how to balance it - I'm just a shitty CSS developer"?

"How do you create a variable-equal-height three column layout using css? ... without tables. in IE6. Write your css on this whiteboard with this marker that's nearly run out."

    .bs-equalheight .bs-responsive .col-md-3
Checkmate, TSA. /s

Now, do it without Bootstrap.

I think he just landed himself a solid 10-15 behind bars.

Id rather land behind bars than code in IE6 again....

Did you miss the "shitty" part?

"Welcome home"

This is exactly correct. When I returned from a weekend vacation in New York a few years ago, Canadian customs asked me about the tourist sites I visited. It's not that they thought attending a musical and visiting the 9/11 memorial was suspicious; it was just a convenient topic of conversation while they watched to see if I seemed nervous or otherwise suspicious.

I always get nervous when passing US border checks.

Once I got asked how many times have you been here, I replied that this is my second time (thinking he means San Francisco), but he said: "It says here that you were in the US 3 times". That really got me nervous, I wouldn't like to get turned away and look for a flight back home.

Do they think that a poor guy at the border can recognize a skilled terrorist? What they do is scare the hell out of ordinary people.

They know that people get nervous. But there's a difference between the nervousness of someone who is intimidated by authority figures and the nervousness of someone who is trying to enter the country illegally or smuggle something in.

Odds of their screening catching a skilled terrorist? Pretty low -- although terrorists generally fall into the category of "bungling" more than "skilled". Odds of them catching people who are smuggling drugs, or entering as "tourists" but actually planning on working? Much higher -- because it's easy to learn to recognize the common cases.

> But there's a difference between the nervousness of someone who is intimidated by authority figures and the nervousness of someone who is trying to enter the country illegally or smuggle something in.

Is there? What's the difference if the emotion is 'nervousness' and the outward expression of that emotion signals 'nervousness'? Who is skilled enough to distinguish between the two degrees of nervousness?

> Who is skilled enough

Someone who spends 40 hours a week practicing.

How much feedback do they get from this practice though?

If you were a 'bad' border protection agent, and you let everyone through, how do you learn? And equally if you select people for secondary interrogation that are allowed to enter, how does that feed back to you?

I guess I'm curious to know a bit more about how the organisation is structured, as there's equivalent in tech discussions, "Ten years experience vs. one years experience ten times." Without some structure to know when you're doing it wrong or right, you can be talking to people for 40 hours a week and not get much out of it.

One way would be to use "known suspicious persons" as training material. Build the system used by the agent so that it does not immediately notify when the passport for such person is scanned, but instead let the border guard do the chatting and only indicate a bit later in the process this person should not be let through.

A bit similar method is (or was) used to keep the X-ray machine operators at airport awake. Software superimposes images of prohibited items on the X-ray image [1] and operator is supposed to notice them.

The other case (false positives) would be harder to tackle on the case or border agent. Maybe it would help if the same agent was actually involved in the detailed investigation and not just responsible of flagging suspicious people.

[1] http://www.nature.com/news/2004/040116/full/news040112-15.ht...

Agreed. False confessions are an excellent example of this.

Odds of them 'catching' someone who is just shy and nervous? Even higher - there's no negative feedback when you turn away someone who was just a tourist, after all.

It's not about recognising a terrorist, it's about recognising a liar and uncovering information.

>it was just a convenient topic of conversation while they watched to see if I seemed nervous or otherwise suspicious.

Is this acceptable? Is there any correlation between "criminal" or "terrorist" and "acts nervous at border"? Are common border guards trained well enough to distinguish these subtle cues if they exist?


It's very easy to spot when someone is nervous, there's nothing subtle about it.

If you're twitchy, talking fast, sweating and can't answer questions accurately about your job or a place you've just visited, then yes I think that is absolutely suspicious and worth investigating.

I don't know about 'Correct'. When you enter Australia you never even talk to anyone anymore - immigration is all done via self-serve kiosks.

Though they still do the odd manual stop and search in my experience. When my son and I were returning from Singapore a couple of years ago, my son had bought a guitar over there and had it in a gig bag strapped to his back in the immigration line as we came back into Australia.

Immigration let everyone through without question, but as soon as they saw him with the guitar they asked him to step forward to an inspection point. I went along to observe, and it was quite interesting. The guy and the lady at the inspection desk asked him to put the guitar case flat on the desk and open it to remove the guitar.

While he did this, I noted that they never took their eyes off his face. They never even glanced at the guitar or the case. He was halfway through taking it out when they told him it was all OK and to stow it away again and be on our way.

I had always heard that the officers watched for your reaction which 9 times out of 10 gives the person away if they are trying to hide something, but this was the first time I had witnessed it first hand.

For the select few with the right citizenship. Everybody else queues up to talk to immigration. During busy time it can take 2h. The self serve kiosks are not the norm.

Travelling to Australia as a New Zealand citizen is about as easy as it gets. My last flight from Sydney to Auckland I was at home 45 minutes after the plane landed.

This has become a lot better in the US now too - I can use my Australian passport at their self-serve kiosks when travelling on an ESTA that has a renewal.

You still have to talk to the immigration officer though - everyone does.

I went to Australia and there are still passport officers. The last one told me she liked the joke on my tshirt. But again, in Australia when there's a terrorist attack, they create an #illridewithyou trend on Twitter... Not everything is pink, but they at least have a good go at trying.

They still swoop in and perform random tests and interviews on people, even happens when you're a Australian citizen LEAVING the country. Last time I flew to LA, I had a customs guy give me a really limp-wristed frisking.

Canada has self-serve kiosks for the paperwork, but they print a ticket which you hand in to an agent, and (depending on how long the line is) they usually ask a few questions before they wave you on.

In Australia (for certain nations only apparently) you never talk to a person.

I agree. I once was returning to the US via Newark airpot (in New Jersey) and the agent asked me what subway stop I lived by since I lived in NYC. I knew that I could have responded any answer, so he just want to see how I would react.

Once I was returning from a year long trip where I visited 16 countries. Too many for the immigration form, and half of them were visited on another passport (dual citizen). Immigration asked me what country I visited and hesitated a bit. Then I told him that I did not know how to answer since I have been traveling around the world!

Sorry but that is the worst idea ever. CS is a far too wide a subject and border agent is a pen pusher who does not possess competence to ask any questions on that subject.

I know several engineers who are very good and probably have never heard of BST because they are too busy writing CSS or designing circuitboards.

This is done, to mainly deter people planning to jump visas. People show fake experience to get a visa. We have a mini industry in India supporting such jumpers. Though the numbers have reduced.

I'd love to know if there are as many false positive detainments for no apparent reason in Israel as in the US (percentage-wise of course) - because all the people I know who ever travelled there found the security measures to be "maybe a bit much" but never "ridiculous, while also a total security theater" like in the US. Or didn't I just hear the stories?

+1: On more than one occasion I've had to fly without my driver's license, and the agent has always grilled me with the clear intent to see if I'm lying.

1. Why'd you lose your wallet? [Uhh...?]

2. When'd you lose it? [At a software conference this past weekend]

3. What languages do you know? [Ruby, JavaScript, Java, Some C]

4. So how many days ago did you lose your wallet again?

And what's wrong with that?

oddly enough, I'd probably get more attention from border agents than my actual colleagues.

I wonder how long they'd put up with my ramblings about memoization and search optimizations before they let me through. :P

Wouldn't a deceitful person just claim to have an occupation that they are actually knowledgeable about? This is basically just taking a test where you get to pick the subject.

"It says here you're a... bombmaker. Would you care to explain the chemical composition of C4?"

I think the point is whether it's a good allocation of resources.

Lets say you have two borders. One has a cursory check of documentation, so allows people to sail through. This costs 2X to man. Another has a more interactive exchange, but each interaction takes longer, so costs 5X to man.

So you either pay 5X, or 2X and then have 3X to do something else with. Could you use that 3X to better protect the border through pro-active investigation and analysis?

On the other hand, attempts to do this in the US have led to the "behavior detection officers". And you can Google that phrase for a roundup of how poorly it's performed.

This happened to an Australian guy recently. Was asked to code up some stuff in Python.


What happens if you're a plumber - do they get you to fix a dripping tap?


Is this a joke, or are you so out of touch that you don't think a labourer could have a desire to ever travel?

As a purely leisure traveler, I can't see why anybody would put themselves through the US border system as the start of their holiday. Talk about starting on a downer.

There's currently a huge demand of plumbers in the US, because the president said he wants to drain a whole swamp or something.

and bricklayers

Why would a software engineer want to visit the US?

For example to attend a conference. Things like a "World Plumbing Conference" exist, though I'm not sure if it was ever held in the US.

I was once going through security in Romania when a plumber was in the queue. He'd brought his full tool kit with him, which provided much hilarity for the security personnel as it was obviously full of things you're not allowed on aircraft.

(Not everyone is a seasoned flyer who knows the rules!)

To see which way water rotates when it goes down the drains, of course.

Are you being serious?

Have you seen their toilets? Plumbing nightmare

Perhaps his Princess was in another castle...

I'm sorry, but after the stress of traveling though an airport, I'm not coding anything until after I get home (or to a hotel) and rest.

I'll only code their stupid test if given a good hourly rate and a laptop with a fast internet connection. I won't hesitate to politely say I don't think this is going to work out and leave the interview.

And then they can deport you for doing paid work on a tourist visa!

You are always allowed to get home if you prefer that as long as it's outside U.S.

Sure, defend the ridiculous.

Note the bonus assumption that legal immigrants don't matter and the US isn't "really" their home.

I don't agree with the decision but I would rather code 10 minutes than to buy a ticket and fly back 9 hours to get home. For me the second option would be rudiculous.

Around 2002 we (a group of Russians) were returning with friends from a ski trip in Austria back to Germany. There happend to be a police control in the train. Then I've realized I had no passport with me. The best ID I had was my business card (of course, no photo on it).

So the policeman looks at it and says "Oh, the database department. Which databases do you guys use?" Basically I was able to identify myself with some Oracle and knowing who Scott Tiger was.

The policeman appeared to be an IT drop-out who switched to police.

I'm going to wait for more information before believing this. There have been so many cases of fake twitter outrage that it makes sense to wait a day or two before taking out the pitchforks.

What's sad is that in this climate it's not completely unbelievable that something like this could happen.

I'm not sure it would be cause for pitchforks if true. Immigration officers in general tend to act aggressive and ask weird questions as some sort of attempt at behavioral screening. Canada only cares that tourists have enough money to leave and don't plan to work, but the last time I went, I got asked why there was mud on my car. Seriously.

I personally know Celestine. There are no jokes here.

This is by far the sanest reaction in the thread.

This is totally believable. A friend who went to a conference with me in the US maybe 4 years ago was asked to solve an integral equation.

It makes sense really - I don't know why this would cause outrage.

This authors of this article claim that his employers were contacted to verify his identity. It doesn't necessarily prove that he was asked technical questions, but it was enough for me to believe the tweet http://www.recode.net/2017/2/28/14764064/nigerian-software-e...

Considering this is at least the second case where it's happened, why do you need to "wait for more information"?

Something similar happened to me around 5 years ago. I'm a white 20-something male and was returning from Colombia on my own, with no bags except a small backpack. I guess that seemed suspicious enough that I was asked specific, quiz-like questions about my profession, and then sent to secondary screening.

In other words, this does not seem to me like anything new.

I think there's been quite a bit of overreaction here.

Part of their job is simply to determine that you are who you say you are. They do this every day - within reason I expect they can ask you any arbitrary question related to you and your life to observe how you respond. They just want to catch those out that aren't, for whatever reason, being genuine about their story. I think there's a false assumption here that somehow @cyberomin's ability to actually _solve_ a BST was in some way tied to his likelihood of entry. That's obviously ridiculous. I imagine his response was still genuine enough that they believed him. Frankly as another commenter joked, I think they could have asked him to prove P=NP. It's when you reply confidently with an 'obvious' solution that they might raise an eyebrow.

Yes it would be unreasonable if their ignorance actually lead to you being denied entry. But in not one of the experiences here, or with @cyberomin, was that actually the case. The thing is, of course, that they're aware of their ignorance and the absurdity of their questions. You see, they know that they're bluffing. That's kind of the point.

It is, perhaps rather unfortunately, part of their job to make you feel uncomfortable, ask probing questions and weed out inconsistencies in your responses. Isn't that part of professional questioning? I can understand the frustration at the abruptness of the questioning, and it's hardly a friendly welcome. I've been angered leaving immigration before and I have to remind myself that ruffling my feathers is all part of the act. When first complaining to a friend she asked, "what did they insult you or something?" Actually, no. They just asked me lots of questions.

Clearly I'd like to think some questions are off-limits - I know there have been justified concerns about this - especially recently. And I understand this is hot topic right now - precisely why I think we should be careful - more careful than ever - not to overreact. From what I observe: The guy arrived, he was asked questions about his profession, his answers were evidently sufficient and he was let in. It happens to thousands of people every day. Honestly? I don't think there's a story here.

The problem is that there are infinitely better questions to ask - like, "oh, what's your day-to-day like?" or "who do you work for? what do you work on?" - rather than terrible technical questions.


> I think there's a false assumption here that somehow @cyberomin's ability to actually _solve_ a BST was in some way tied to his likelihood of entry. That's obviously ridiculous.

You just got off a plane. You've been in the air for the past 23 hours. The agencies in charge of border security at your arrival airport have a reputation, and a well-deserved one at that, for (1) harassing foreigners, (2) having unclear policies, and (3) more recently, having no idea what the actual law is (or actually outright disobeying it).

Still think it's that ridiculous?


On top of that, there's a long history in our industry of people reading questions and answers off pre-prepared lists and saying "oh, your nuanced, correct answer doesn't match up with what I've got written down here - sorry, I'm trashing your application".

While it would absolutely disgust me to see the TSA/CBP use something like that, I would also be completely unsurprised to see it happen - especially if it happened to a non-US citizen, since they have next to no legal standing in the U.S.

I think this gets to the heart of how so much of this discussion misses the point. The question is not about solving CS problems. It's about determining the authenticity of the passenger's story. In this example, provided that the border agent is at least sufficiently aware that a BST question is a 'hard problem', the question may have simply been posed to observe if the passenger reacts appropriately to that. Even if the answer is "look, I've just been on a plane for 23 hours! you couldn't possibly expect me to..?", You're right, the agent couldn't. Tick! The response is consistent with the passenger's story.

It's a bluff. Which is to stress a more important point: it's not for us to second guess the subtleties of a border agent's questioning. That's part of their professional training. -- That is of course, unless we have cause to believe the questioning is in some way unethical. And you raise (1), (2) and (3) that are clearly examples of unethical behaviour. But with respect to this story - where is the evidence that any of this happened? [1]

This is _precisely_ why we should be careful not to generalize and be accurate in our criticism - if we are to be taken seriously in an area where there is understandably much cause for concern.

[1]: To be clear: A technical question about a passenger's stated profession is not unethical. Yes, it would be unethical if the quality of the _technical_ answer was somehow tied to admittance. But again there's no evidence that that happened.

That's a far too level-headed and reasoned response for the current climate, even in HN.

Returning from Canada back in the 90's, I was asked what I had been doing there.

"Attending a conference on computational geometry."

"What's that?"

Pause for thought -- several seconds.

"Applying computers to solving problems in geometry."

This got me waved in. Co-workers told of the encounter later on proposed an alternative reply: "You wouldn't understand." Given the tone of the agent, those might have been very costly words.

Could have been worse. If you had been at a conference on algebraic geometry, you might have been the mathematician who started talking about blowing up points on the plane while in the security line up...

And algebra is an arabic word after all. No good can come of that.

After watching too many episodes of border patrol-like shows, I agree that it would be a very bad route to take: If you are demeaning, they'll only dig deeper; if they "don't understand" they _will_ find someone who does, or take your phone and call your boss to find out.

I want to joke that CBP might be looking for referral bonuses by referring great candidates to tech companies.

However, if it's really true, it is depressing. He was actually given an A4 sheet to balance a BST. Wow.

What if he failed the test? I assume that CBP cannot deny you entry because you didn't brush up on your algorithms and data-structures during your flight. But, they can still keep you detained for secondary screening.

This is what happens when you have a populist president, people start disregarding the law and listen to the President even if he/she is wrong.

Imagine this happening at the time when companies are starting to accept that you can't interview candidates solely by asking them to solve algorithms on a whiteboard, then some inexperienced staff go to Wikipedia and expect people to be able to recite it.

The question's what happened as he said he was too exhausted, does he get flagged for secondary screening? The travel ban is suspended AFAIK.

We are witnessing self-division at sad levels. We had a flare up of xenophobic attacks in South Africa last week. In an earlier incarnation of such attacks in 2008, mostly Zulu people would ask you what certain things are in Zulu, and if they perceived that you don't know what they are, they would accuse you of being a foreigner, and anything could happen to you. An example that became popular was "what is an elbow or knee in Zulu?". I'm not making this up, and this happened in a country with 11 official languages.

The point I'm getting at is that this lawlessness started because a populist president and other leaders started shooting from the hip, making inflammatory statement and playing political football with our lives.

Trump is worse IMHO as he signs an Executive Order and things go crazy until the courts can act. You should worry when your first citizen is not well-acquainted with your Constitution like our dear Jacob Zuma and your Donald Trump are. The country ends up being run through the courts, and the courts don't act expediently.

Is there any evidence that this guy was specifically singled out for being non-white, or that this has anything to do with Trump at all?

Border guards are allowed to ask you questions to see how you react and to corroborate your story.

If someone (from any country) entered claiming to be a physicist, would it be reasonable to ask him to try to solve some integrals?

No, it wouldn't? What does a border guard know about calculus, much less some physicist's particular area of research? The whole reason this is farcical is that self-balancing search tree algorithms are notoriously based on multiple balancing cases and it's ridiculous to expect someone to have memorized them. Some even rely on amortized bounds which only complicates the implementation and explanation further.

Even ignoring the border guard's competence, there's a difference between being able to solve problems and being able to solve problems after traveling for 23 hours straight - as @cyberomin said he had been. Maybe if it's pure recital from memory, something so basic that it should come to mind automatically without active thought (self-balancing trees are not even close), then I might trust myself to answer while sleep-deprived to that extent; but even then, I might easily make very stupid mistakes. If solving the problem requires even a bit of active intellectual effort, then forget about it; I'm too tired for that shit.

How would a border agent even prove they possess the necessary skills and knowledge to even verify the veracity of an answer? As a tech consultant who spends inordinate amounts of time explaining to clients various kinds of plausible-sounding bullshit from others, I seriously doubt border agents can fare better.

That's not the purpose of questioning - the answer doesn't matter, it's how the questions are answered.

How are immigration officers supposed to do their jobs? The purpose of immigration officers isn't to just blindly stamp passports; they actually have to determine if the person attempting to enter should be allowed to enter. Which interestingly, is the job of immigration officers across the world.

I feel like people are just looking for fight and begging for something about which to be outraged. Immigration and Customs officers from all countries have been doing this as long as there have been Customs and Immigration.

You could give any answer to those kind of questions and as long as you seem confident and sound truthful, you breeze past and aren't given a second look. The CBP officer might just happen to be knowledgeable in your field enough to be able to verify your answer or he may have no clue and just pulled a question from his ass. They are just looking for a reaction and the tone of your answer.

Well, they might have the key. If your answer does not match the answer in the key, BAM, you are not allowed.

(Not saying that this is the correct approach, just saying that this is possible if correctness is not a goal.)

I never said he was singled out, or by race/ethnicity/color even.

Whether this relates to Trump: As others have pointed out, yes this has been happening before Trump, I'm not alluding to Trump being the sole cause. The point that I'm making is that leaders (president and even local leaders) who can make statements or take actions that are contrary to the country's laws have an effect on the guy on the streets. If you tell me that foreigners are taking our jobs (regardless of its truth), I might not be very objective as a CBP employee. I might even be biased against certain people, but that's hard to judge as we are different as humans.

The guy on the tweet said he was asked 10 other questions, and they seemed to expect textbook/Wikipedia type answers. A blog post from him will hopefully have more details for us to make better observations. You make a fair point about the physicist, but everything in moderation is fair.

My point if any, is that what leaders/politicians say affects our attitude and often opinions. Whether we like such leader or not, I hope we can agree on that at least.

This story has nothing to do with Trump, his policies, or rhetoric. CBP tries to assess if a story is valid, this sounds like some kid who took a few classes being a dick. Stop trying to make every little thing about Trump because of your personal bias. You sound just as ignorant as the idiots who tried to pillory Obama at every turn.

> This is what happens when you have a populist president

Spare me. This stuff was happening pre-Trump, and it will happen post-Trump.

Care to provide a citation for people being asked hard algorithmic questions by CBP before?

To be clear, I don't think Trump is directly responsible for this. But I think he's sent a signal to fascists and racists around the country that America is for white people and it's okay to throw your weight around. He's a bully, so he's emboldened other bullies (which, unfortunately, dominate law enforcement).

> But I think he's sent a signal to fascists and racists around the country that America is for white people and it's okay to throw your weight around

You have that exactly backwards. He was voted in legitimately by the right and center because the left failed to do anything to address their grievances, justified or not, and circumstances.

Trump (and Brexit, etc.) is the signal that the public is sending to the left and may heaven help us all because we're sure going to need it.

I think the reasons Trump won and the message he's sending in office are, in fact, different things. There were a whole lot of unhappy Trump voters (people voting for him despite lots of reservations about his policies and demeanor) and a lot them were due to the left not addressing their grievances.

That doesn't change the fact that his rhetoric has emboldened hard-right fascists and bullies. It's inarguable at this point.

I'm not sure I follow... the parent comment didn't seem to question the legitimacy of his election. And I also think that Trump's attitude in general can be seen by many as a validation of that behavior ("throwing your weight around" / bullying).

When I applied for my TN I had to convince the border guard I could do the job. I didn't have to balance a binary tree but I did have to name drop CS concepts.

There are a number of examples on this page of it happening previously and in a variety of locations.


Really? As an immigrant who came here for a programming job and has been through immigration many times, this has never happened to me and nobody I know has ever mentioned it in the conversations we have complaining about how annoying CBP are. How common do you think it is exactly?

Did you read my comment at all? I literally said Trump is not directly responsible for this.

And no, I do not think any or even most programmers should be expected to know how to balance a binary tree on demand.

> Did you read my comment at all?

Yes, and I did us both the courtesy of not drawing attention to or responding to the cringiest parts of it. Others have provided stories of similar stuff happening under other presidents. Case closed.

'morgante asked specifically for a reference and explicitly stated they didn't think Trump was responsible. You didn't provide a reference and asked if they were insinuating Trump was responsible. Why did you choose to (a) not provide a reference and (b) ignore the statement that Trump wasn't responsible? Why choose to comment at all in this case?

It was a loaded, disingenuous question. It was one already answered several times in this thread. The very premise of the question was ridiculous to start with. It also came attached to a left-wing conspiracy theory.

I would have been better off not reply to such drivel - thank you for reminding me.

Other than the last bit where they express an opinion, I didn't take it that way at all, particularly as 'morgante specifically took care to include the statement regarding Trump not being responsible. There are quite a few people in this thread (myself included) who are not well-versed on a lot of the details that may go on during customs interviews. Having references (other than something someone said on some internet forum) is commendable—to me the antithesis of someone searching for a conspiracy.

And if you thought it was disingenuous, and chose to answer anyway, don't make it worse: the goal should be to improve the conversation.

Perhaps you thought they should have already known about such things, or that they should have looked them up on their own. You mention that it was answered elsewhere in the thread: you could have referenced those comments as well. but choosing to respond like you did does nothing to improve the discourse.

Literally my second sentence was "I don't think Trump is directly responsible for this" and then you go and accuse me of insinuating secret executive orders.

You should be banned for an argument that disingenuous.

Very frustrating, indeed. I'm not sure if banning is appropriate. Refraining from engaging in the future would probably be more prudent.

It's probably time to revive my HN blocklist extension. [0] Banning is potentially going too far, but there are certain accounts which continue to not debate in good faith and contribute negatively to the discussion.

[0] https://github.com/morgante/hn_blocklist

Do you have a citation supporting bullies dominating law enforcement -- specifically Immigration enforcement officers?

Thanks, you made the point better than I could have. I'll validly get some flack for starting out by linking my comment to POTUS, which is good as it teaches me to reason much better with sensitive topics where there's often no objective answer.

This is what happens when you have a president you don't like. Everything you don't like around you becomes their fault.

It happened before Trump but there is no way that someone aggressively calling for greater immigration enforcement isn't going to be encouraging border agents to do whatever they think is "greater enforcement" and as we can that greater enforcement is mighty arbitrary.

So, it's "yes and no but mostly no"

People have been asked CS questions at airport security earlier too?

First, this wasn't airport security, this was immigration. Secondly, CBP officers routinely ask questions to incoming passengers -- even to Americans! Binary Trees? I don't know -- but neither does anyone else because we're talking hundreds of thousands of people per day and only a self-selecting few post their encounters on Twitter; all of the oil field workers returning from Africa probably aren't posting their every encounter with Immigration on Twitter. People having their bags ripped apart by Thai Customs aren't likely getting featured on Hacker News. How are Serbians treated when they transit the Frankfurt Airport? I have a friend who is a designer who was asked to open his computer and show some of his designs and I have had others who entered Germany/France with no problem. Most people don't post play-by-play of their travel experiences -- so we see a very narrow and potentially inaccurate view based on stereotypes and anecdotes rather than fact.

All of this "anecdotes are now valid data" nonsense seems to be contradictory for a group of people who purport to be interested in software engineering and the implied respect for statistical validity that would encompass.

Why is this even a story? Immigration officers ask questions to detect inconsistencies -- nothing at all new about that-- nothing even wrong with that. The guy couldn't even answer it and was still admitted. If he was arrested because he couldn't solve binary trees, now THAT would be a story.

> This is what happens when you have a populist president, people start disregarding the law and listen to the President even if he/she is wrong.

Where are you getting this from? You're linking the questions supposedly asked to someone entering the US to the president that was inaugurated a little more than 30 days ago, who has not passed any kind of legislation or EOs that would have any impact on what border control agents ask their clients.

> The point I'm getting at is that this lawlessness started because a populist president and other leaders started shooting from the hip, making inflammatory statement and playing political football with our lives.

Zuma has been in power since 2009. Ah yes, I remember the SA of 2008, such a peaceful, strife-free wonderland.

I'll presume you to either also be South African or at least following politics here. Yes, Zuma wasn't in power, but this was around campaigning time leading up to 2009. The violence wasn't pervasive around most of the country, but was in many people's post-analysis linked to local politicking.

The country wasn't different between 2008 and 2009, but as a township living black South African I can tell you that because of what populists have said, and the role of the media incorrectly reporting to click-bait us, things have gotten worse.

To answer your first question, many people have posted that this has been happening in the US, what I'm saying is that if a senior political can say something popular yet Constitutionally incorrect, people who have the "power" to act on that will use their power.

I'd speculate that they're really just looking for any indication of understanding the question, rather than a complete and correct answer. To the extent that's true, it's not entirely unreasonable.


Do you have any evidence that this just started ~30 days ago after Trump's inauguration? It's entirely possible -- likely even -- that this has been going on for quite some time and the media is just more interested in reporting on it right now because they know it'll play into the Trump narrative.

That doesn't justify the actions in any way, but it shows you how powerful the media are at forming narratives -- and how easy it is to fall for the trap.

I think Trump may have kickstarted that narrative, because of that whole thing about Mexican immigrants (and some of them I'm sure are nice people), and how he banned the citizens of 7 countries from returning or entering the US.

I think its fair to say this kind of treatment of people is nothing new - but to say the media is "forcing" a narrative here is hard to swallow. Trump has made it, at the very least, incredibly easy to create a narrative of racism for his detractors and the richard spencers of his supporters.

Let's back up a second: "Mexican Immigrants != Illegal Immigrants" One is a subset of the other and Trump's rhetoric was directed at illegal aliens and not "Immigrants."

Allowing an innacurate narrative to propagate is part of the problem.

"When Mexico sends its people, they're not sending their best. ... They're sending people that have lots of problems, and they're bringing those problems with us. They're bringing drugs. They're bringing crime. They're rapists. And some, I assume, are good people,"

Commencement speech quote. "When Mexico sends its people" doesn't sound particularly specific to illegal immigrants.

Trump at the very least made it easy to form this narrative.

ed: “Trump is a white nationalist, so to speak, he is alt-right whether he likes it or not,” Spencer in a recent interview on “The David Pakman Show.” http://www.haaretz.com/us-news/1.768982

Its true of the MSM and the far right.

Trivial observation:

I suspect Trump deliberately chose the words to cover both bases. (Well, to the degree he can deliberately do anything, that is.) It sounds like he's referring to all Mexicans, which satisfies his alt-right supporters. Meanwhile the more scrupulous supporters (or even unscrupulous ones when they want to play semantic games) could plausibly interpret the words to mean only "illegal immigrants", thus denying racism at the heart of Trump's campaign.

"Take him seriously, not literally." Worked wonders for him.

I don't know, and neither does anyone else because the people who are able to look into this are either running the show (the administration) or don't want to investigate (the Republicans in Congress). The best that the media can do is collect anecdotes and submit FOIA requests to see what they can find out.

There's no trap to fall into, I can literally pull up YouTube clips of Trump scapegoating immigrants at a moment's notice.

Awful shit that happened under Obama (of which there is no shortage) is on Obama. Now? Trump owns it.

The guy appears to have successfully entered the US (his tweet was sent from Manhattan), so apparently he passed their test.

He also explicitly stated that he refused to answer the BST question and they moved on to other questions.

Meaning it's not even speculation to claim that they weren't requiring an accurate answer to the BST question for entry: it's demonstrably true fact.


Yeah, I mean it's not like they did the same thing two weeks ago:


Or harassed and intimidated a 70-year old children's book author:


Or almost deported a visiting Holocaust scholar:


Or maybe, just maybe, I come from a family of immigrants who has seen people around him treated this way even before we elected a racist reality tv star as POTUS.

It's against HN's rules to use the site primarily for political or ideological battle, so please don't do that.

You've obviously got some good reasons for feeling this way, but the way you've been using sarcasm to vent them is not helpful. It limits the upside to provoking indignant agreement from those who already agree, and amplifies the downside by basically throwing lit matches at a petrol station.

Difficult as these divisive topics are, HN is committed to trying for thoughtful discussion and we need everyone's help with that.

I apologize and will try to do better.

Thanks—seriously appreciated!

Stuff like this happens all the time, the press never picked up on it until Trump came into power. I posted a story of a close friend who got denied entry at the border and banned for 10 years. I've heard other stories where friends of friends )I met them and talked with them) were accused of being strippers or hookers flying to Vegas and being banned for 10 years as well. All during Obama's time, so it's not new. Border guards are facists.

And all 3 of those stories you provide are non-Muslims, and 2 of them are white Australians, so it's not directly a "racist" event.

There was also Mohammed Ali, Jr. this past weekend who was a US Citizen but still got detained. A schoolteacher from England who was refused entry, a Canadian Student-Athlete was was refused entry two weeks ago, all three of these are Muslims. Also, at least two US Citizens who were denied global travel cards even though they were businessmen who travel frequently, both Muslims.

And it doesn't have to be a "racist" event. The administration literally said they wanted to "ban Muslims", this could be exactly the policy they wanted when they passed the Executive Order. And the only way to tell is to get Congress to do more digging.

Global Travel cards? You mean Global Entry? The requirements for that program are rather strict -- lots of people are denied those, but only the Muslim denials make the news? How does Global Entry know someone is a Muslim? It isn't on the application.

Here is the link: http://www.teenvogue.com/story/muslim-travelers-entering-the..., you can judge for yourself about whether the policy was fairly applied or not.

The Administration opened themselves up to the question of whether they are unfairly targeting Muslims when they said they wanted to "ban Muslims" from coming to the U.S. and with all of their heated rhetoric on the campaign trail.

Ask Maher Arar what CBP is allowed to do, or better just read up on the case. Don't assume the laws in this area have any relation to what you would hope they are. They're not.

If you are not a citizen, the CBP can deny you entry for pretty much any reason. If you are a citizen, they can detain you but not deny you entry indefinitely.

> I assume that CBP cannot deny you entry because you didn't brush up on your algorithms and data-structures during your flight.

Sure they can, if you're not a citizen or permanent resident.

I read half the thread and still didn't see a point, so I'm doing that. They do not try to see you fail at balancing bst. They see your reactions on irrational things. They know it is irrational and ridiculous. Anyone who talked to police/immigration/security officer knows that they are always the same — because if discussion is easy and rational, you can't tell if someone lies. All those "look for body signs" methods are bullshit.

I'd get suspicious and ask why he'd not stay in IT and whether he isn't actually trying to infiltrate the TSA.

Not as spectacular, but 4 years ago when I arrived at SF airport after a 11 hour trip the immigration officer asked why I was there. I told them I was visiting a software conference. To my surprise he then asked me to write 16 in hexadecimal. Luckily I didn't screw up.

I asked him how come he knew about that stuff and he told me that in a former career he was working in IT as well. I thought it was funny.

I was just overcome with anxiety...the answer is 10, right?

yes :)

Goes to show you never know what someone knows from their previous life experiences, and that you should not judge a book by its cover.

Given how poorly academics, research and other fields pay, I wouldn't be entirely surprised to find that there are highly educated people trying to make ends meet working for the TSA or Customs. And odds are they are eager to dust off that knowledge and put it to use when they can.

December 2016, I arrive in JFK from Moscow and a border officer asks me about the purpose of my visit. I explain that I attend the business meeting in NC. She wants to help and informs me that I have to pick up my luggage in NYC and then check it in for my next flight. I smile and reply "fortunately I don't have any luggage". Immediately she becomes suspicious of me and asks "But you are here for a business meeting, where is your business suit?" I explain that I am IT and everyone in my company is OK with a casual style". She nods and let me go. "Thanks God IT does not really care about my clothes" I think and successfully enter the land of the free.

Plot twist: she knew you didn't have any luggage all along. That information is available to her when she pulls your info up on her computer.

In JFK there 2 modes of going through the passport control : the old one involving an officer with a computer, fingerprints scanner and camera and the new, automated one that involves you interacting with a kiosk that prints some kind of voucher at the end. This voucher then is given to an officer who does not have a computer, but she usually asks a couple of extra questions. I used the new way, I like it. So perhaps she didn't know anything :-)

I have a theory on how CBP is trained to scan people, that seems more plausible without assuming malicious intent: they're not expecting you to know exactly how to balance a BST, but just enough to hold a conversation about it while they look for telltale signs. My guess is that even a reply like, "Look, I'm a self-taught web developer and I don't deal with algorithms day-to-day, sorry. But you can ask me web dev questions if you wish." would work.

Agent: "wrong answer,you are not allowed entry, good bye".

What reason do you have to believe this would happen?

In many government jobs, the criteria for moving a task forward is the ability to check off a tick box. So you do not admit you do not know the answer; you give a plausible answer that lets the officer check the box. That's the case for most govt questions. Very little depth is required in the answers as not everything can be validated in the timespan of an interview. So admit you know what a binary tree is and talk about it in high level terms. Unless the officer was a previous programmer, the checkbox gets checked.

When you say you do not know or answer a different question, it makes it harder to check that box off. Most officials just want to check a box and move you (and themselves) on. Don't make it difficult for them.

You assume that the box says next to it "can answer questions about his career specialism correctly". It probably doesn't. More likely it says "does not appear nervous when asked about his career specialism, and appears to know topics he claims to know" or something more like that.

Sounds like your assumption, not fact.

Not even close, but similarly: travelling to Israel for work some years ago I was asked what I did for a job. Software engineer, I said. 'Where is your laptop?' I explained I didn't have one, that I worked only on desktops. It took some persuading the guy that you could be a software engineer without a laptop.

I flew to the USA late last year, through London. When going to the desk for my connecting flight at LHR, the gentleman there did some sort of pre-authorization and asked me a number CS question. Nothing as specific as the above, but things like what languages I used for work, specific tooling, who my clients were etc. It felt quite strange to be asked these things, it's never happened to me before when traveling anywhere including stateside. What's more, this was a person hired by American Airlines, not some CPB officer – or, at least, it seemed that way.

Airlines do a CBP-type interview before letting passengers board to make sure that they will actually be able to clear US immigration. If CBP decides not to let someone through, the airline has to pay a fine and the return ticket.

Is it possible the person was just curious/interested?

I thought so at first as well, he seemed curious but kind of prying, so I asked whether the questions were necessary. He answered politely but sternly that yes, yes they were. After that, it was a bit awkward and stiff but still quite polite. It all just seemed very strange, I've never been questioned like that before.

Once I got to the states however, the only problem I had was that lines were long. The CBP officer handling me and letting me in to the country was very nice and polite, and after the usual "business/pleasure?" and "how long are you staying?" questions etc. I was let in to the country with no issue.

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