I confess to being unfamiliar with a lot of the terminology that Fred uses here. If he felt like elaborating on what all these things mean, I would be grateful. —Dan ----- On Nov 3, 2020, at 2:38 PM, Fred Lunnon <fred.lunnon@gmail.com> wrote: Worthwhile perhaps to clarify explicitly that a generalisation of Dan's observation yields the decomposition into axial coplanes and "angles" of an isometry in a general quadratic geometry --- for instance, projective n-space with homogeneous coordinates incorporating translations; Minkowski space (mathematician's conformal), boosts having imaginary "angles"; contact geometry (physicist's conformal, "oriented spheres"). -----