proposition: Fact pair_scale1 u : scale_pair 1 u = u.
proof: Proof. by case: u => u1 u2; congr (_, _); apply: scale1r. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)