This reminds me of a mathematical joke.
"Either you believe in the law of the excluded middle, or you don't".
It was the email signature of a logician (a colleague) and it took me ages to get it.
Here's another:
"There are 3 kinds of mathematician. Those who can count and those who can't."
Also:
"There are 10 kinds of people in the world: those that read binary and those that don't."
(In binary code 10 = #2)
