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Worked in HFT and funds, there's a bit more to the taxonomy:

- Trading completely based on the current prices. If you're doing purely arbitrage, eg looking for the ask to go under the bid (elsewhere), you are gonna have to be really, really fast, because that kind of thing is so very obvious nobody hasn't thought of it.

- One step from from that is passively leaving an order in and hoping for the same thing. Eg you leave a bid in a less liquid market, below the bid in the main market, and hope someone hits you. You then immediately throw that onto the main market. Gotta be super fast to do that, because of course everyone else can see someone traded.

- Market making based on some form of ML on the orderbook, basically imbalance. Here you need to do more than just comparing two prices. You also aren't entirely leaning on the current price to offload your position, you might hold onto your position a bit. So now there's risk involved, and you might need to decide how big a position you want. And not everyone will have the same position, so not everyone is after the same trade.

- Market making based on multiple orderbooks. Say you have an ETF basket, and you want to be able to make bids and offers around it, as well as the underlying shares. So then you have a different position to everyone else, there's a fair bit more information to digest, and there's a fair bit more modelling which will mean different participants have different decisions. This means your decisions will not be contested in the same way that obvious arbitrage would be.

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