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If your chest of drawers has two drawers and you put three items of clothing in them, at least two items—possibly all three—must end up in the same drawer. This seemingly trivial observation is actually the basis of a powerful reasoning tool!
We know that mathematics can be a source of joy, but have you heard of happy numbers? Simple to define, they hold plenty of surprises and show just how much playing with integers remains an inexhaustible source of research at every level.
Ramsey theory is another field in which Erdős played a crucial role without being its originator. His use of the probabilistic method was essential to this theory, whose aim is to find the size of a set that guarantees the existence of a substructure possessing a given property.
