proposition: Lemma expr1n n : 1 ^+ n = 1 :> R.
proof: Proof. by elim: n => // n IHn; rewrite exprS mul1r. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)