Question 116
A *lattice point* in the Cartesian plane is a point whose coordinates are both integral. A *lattice polygon* is a polygon whose vertices are lattice points. Let $\Gamma$ be a convex lattice polygon. Prove that $\Gamma$ is contained in a convex lattice polygon $\Delta$ exactly one vertex of which is not a vertex of $\Gamma$, and the vertices of $\Gamma$ all lie on the boundary of $\Delta$.