The inspiration for the name of this mathematical principle: pigeons in holes.
Here n = 10 and m = 9 so we can conclude that some hole has more than one pigeon.
Also known as Dirichlet's box (or drawer) principle, states that, given two natural numbers n and m with n> m, if n items are put into m pigeonholes, then at least one pigeonhole must contain more than one item.
