HN submission. Found in a submission link or body. Submitters do not count as commenters in the main ranking; a submission is not an endorsement.
Abstract
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.
arXiv comments
5 pages; this will eventually appear as an Intelligencer article. This is a replacement of yesterday's submission, and differs only in that I changed the abstract