25 May
2015
25 May
'15
2:32 p.m.
If the sum S of the 4 corner solid interior angles are used, then Propp is wrong. A flattened sliver tetrahedron has S=0, a flattened regular tet has S=2*pi, etc. there is no constant value. Propp presumably meant, the 4 tet faces viewed from a point inside; then obviously the "whole sky" has total solid angle 4*pi, the end.