In "A mathematician's Miscellany", By J. E. Littlewood, I found this piece of conversation between Littlewood and Wittgenstein:
"Schoolmaster: Suppose x is the number of sheep in this problem
Pupil: But, Sir, suppose x is not the number of sheep
(I asked professor Wittgenstein if this is not a profound philosophical joke, and he said it was.)"
I'm not familiar with the works of Littlewood nor Wittgenstein, so I'm not sure how to interpret this joke. Maybe it's something much more simple than it looks but I'm honestly confused about the profound implication of the joke that Littlewood mentioned. I would really appreciate it if someone can shed some light on me.