Pan Galactic Division

This is a light expository article. It explains a proof, due to Peter Doyle and Cecil Qiu, the following result from set theory. Let A and B be sets. Suppose there is an injective map from A x {0,…,n-1} into B x {0,…,n-1}. Then there is an injection from A into B. Unlike previous proofs, this one is a very simple one.