fact: Definition between (x y z : Plane) := [&& (det x y z == 0)%R, (0%R <= scalar_product (x - y) (z - y)) , (0%R <= scalar_product (x - z) (y - z)) & ((y == z) ==> (x == z))].
imports: mathcomp(all_ssreflect ssralg matrix ssrnum vector reals normedtype order boolp classical_sets) counterclockwise