proposition: Fact pair_scaleAr a (u v : A1 * A2) : a *: (u * v) = u * (a *: v).
proof: Proof. by congr (_, _); apply: scalerAr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)