Lattice Polygons and the Number 12
1. PROLOGUE. In this article, we discuss a theorem about polygons in the plane, which involves in an intriguing manner the number 12. The statement of the theorem is completely elementary, but its proofs display a surprisingly rich variety of methods, and at least some of them suggest connections between branches of mathematics that on the surface appear to have little to do with one another. We describe four proofs of the main theorem, but we give full details only for proof 4, which uses modular forms. Proofs 2 and 3, and implicitly the theorem, appear in [4].