AlgTop10: More on graphs and Euler's formula

We discuss applications of Euler's formula to various planar situations, in particular to planar graphs, including complete and complete bipartite graphs, the Five neighbours theorem, the Six colouring theorem, and to Pick's formula, which lets us compute the area of an integral polygonal figure by counting lattice points inside and on the boundary.

This is the tenth lecture of this beginner's course in Algebraic Topology by N J Wildberger of UNSW.