AlgTop15: Rational curvature of a polytope

We use our new normalization of angle called turn-angle, or "tangle" to define the curvature of a polygon P at a vertex A. This number is obtained by studying the opposite cone at the vertex A, whose faces are perpendicular to the edges of P meeting at A. A classical theorem of Harriot on spherical triangles is important.

This the 15th lecture in this beginner's course on Algebraic Topology given by Assoc Prof N J Wildberger at UNSW.