Dijkstra had a unique format for his undergraduate class where the entire grade basically came down to an interview at the end of the semester. During which he asked you to work out a solution to a problem in front of him one on one. A friend had the most memorable interaction with him during the interview/final exam. Dijkstra explained the problem and they began furiously writing out a solution in pencil getting a few lines into the proof before realizing they had made a mistake and began to erase what was written. Dijkstra responded "tsk tsk tsk, you are a rash mathematician" and advised the student to "Use a pen instead of pencil it will encourage you to spend more time with your thoughts before writing."
A couple years later I saw a quote that reminded me of that interaction and it goes
“I mean, if 10 years from now, when you are doing something quick and dirty, you suddenly visualize that I am looking over your shoulders and say to yourself "Dijkstra would not have liked this", well, that would be enough immortality for me.”
The exam in interview form is called an oral examination (vs written examination) and in my university in the Netherlands they were not that rare, especially for exams in the senior years where class sizes are smaller.
I actually prefers pens than pencils but with different reasons. With pencils you are tempted to erase things. However, it is an illusion; Eraser does not really erase things, ending up in a dirty paper. It also takes much more time. With pens, erasing is effortless and does not require additional decision to make: Just strikethrough it. Then throw it away when you feel you want to start over.
A couple years later I saw a quote that reminded me of that interaction and it goes “I mean, if 10 years from now, when you are doing something quick and dirty, you suddenly visualize that I am looking over your shoulders and say to yourself "Dijkstra would not have liked this", well, that would be enough immortality for me.”
Dijkstra's ghost haunts us all.