(continuing) Hyperbolic Pythagoras tells us \[ \cosh c=\cosh a\cosh b \] (Spherical uses "cos".) I long-ago (re?-)discovered Hyp de Gua: \[ \cos\frac{D}2=\cos\frac{A}2\cos\frac{B}2\cos\frac{C}2-\sin\frac{A}2\sin\frac{B}2\sin\frac{C}2 \] (Sph uses "+".) Beyond that? I have no idea, even for 4-space. Hyp volumes are encoded in elaborate integrals, and a Pythagor-esque relation among them seems quite elusive (to me). So, I thought I'd post this as an #OpenQuestion in #NonEuclidean #Hedronometry