mathlib3

35ca0862 - feat(geometry/euclidean/angle/oriented/affine): signs of angles and sides of subspaces (#17234)

feat(geometry/euclidean/angle/oriented/affine): signs of angles and sides of subspaces (#17234) Add lemmas about the signs of angles, at points on the same / opposite side of an affine subspace (typically a line), between two points in that subspace.