Reminds me of a joke: A biologist, an engineer and a mathematician see two people enter a seemingly empty building, and a moment later, three people leave. Bio

Reminds me of a joke: A biologist, an engineer and a mathematician see two people enter a seemingly empty building, and a moment later, three people leave. Biologist: They must have reproduced Engineer: It must have been a measurement error Mathematician: If one person enters the building, it will become empty