An angle in Minkowski space (Q1882441)

According to Busemann, no particular angular measure can be entirely natural in Minkowskian geometry. There have been many attempts to define such a measure, but none has found general acceptance. This is yet another such attempt. It defines a measure on cones of arbitrary dimension (hence a solid angle), in addition to be additive and invariant under invertible linear transformations (with the defining convex set that serves as unit ball transformed along).