Take a ball, divide it into parts, glue them back and get two identical copies of your ball!
Some interesting observations with the pigeonhole principle
This post was part of the Chalkdust 2016 Advent Calendar. Newton: "Are you going to the Fibonacci themed Christmas party?" Euler: "Yes! I heard it's going to be as big as the two previous years put together."
Behind today's door... The Chalkdust guide to Christmas presents
And on the fifth day, some rather Algebraic Golden Rings:
Cédric Villani’s Birth of a Theorem tells the story of a mathematical theorem
