Use the Konig-Egervary Theorem to prove that every bipartite graph G has a matching of size at e(G)/A(G) where A(G) is the maximum degree. Use this to conclude that every subgraph of Kn,n with more than (k-1)n edges has a matching at least k.
The Konig-Egervary Theorem is used to perform a proof of matching numbers.