my other favourite mathematical joke
A biologist, physicist and mathematician are in a café, watching a house across the street. They see three people enter the house, and a while later four people leave the house.
The physicist says: "I thought the house was empty at the start. There must have been a measurement error."
The biologist says: "Why? They could have reproduced in the meantime."
The mathematician says: "Both of you are wrong. If one person enters the house, it will be empty again."
Mastodon is a server for a federated social network: everyone can run a server if they want to, including me. So this is a Mastodon server for me (Vierkantor) and my friends.