4. A graph G is called planar if there exists an embedding of G in the plane so that no pair of edges intersect, except possibly at shared endpoints. A plane embedding of a planar graph results in a subdivision of the plane, Where each maximally connected region is bounded by vertices and edges of the graph. Each such maximally connected region is called a face. Prove that the complete graph on ve nodes is not planar. Provide citations if you use any known theorems from the literature