Post #1763204

I'm taking a descriptive set theory course. I'm the only one from the type theory group (which is in the CS department), the others are master's students in the math department. In today's exercise session, one of them wrote on the board “{F ∈ ℱ(X) | F ∩ U}” and said that F ∩ U was a shorthand notation for “F intersects U”. Others started to laugh. He said that after all it makes sense because you can convert a set to a boolean through the function that maps the empty set to the boolean false and non-empty sets to true. After some more amusement, he continued the exercise. I didn't say anything.