I am looking for jokes which involve some serious mathematics. Sometimes, a totally absurd argument is surprisingly convincing and this makes you laugh. I am looking for jokes which make you laugh and think at the same time.

I know that a similar question was closed almost a year ago, but this went too much in the direction "$e^x$ was walking down the street ...". There is also the community wiki Jokes in the sense of Littlewood, but that is more about notational curiosities. In order to motivate you, let me give an example:

The real numbers are countable. Indeed, let $r_1,r_2,r_3,\dots$ be a list of real numbers and suppose that there is a real number missing. Just add it to the list.

If moderators or audience decide to close this question as off-topic or duplicate, I can fully understand. I just thought it could be interesting and entertaining to have this question open for at least some time.