proposition: Lemma natrB m n : n <= m -> (m - n)%:R = m%:R - n%:R :> R.
proof: Proof. exact: mulrnBr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)