mathlib

e1d2f5bd - feat(geometry/euclidean/basic): `affine_isometry.angle_map` (#16374)

feat(geometry/euclidean/basic): `affine_isometry.angle_map` (#16374) Add the lemma that angles between three points are preserved by affine isometries, analogous to the one that already exists that angles between two vectors are preserved by linear isometries.