proposition: Lemma T1le_pmulrl x a: x != zero -> a <= x * a.
proof: Proof. move => xnz. by rewrite - {1} (T1mul1n a); apply:T1le_mul2r; rewrite T1ge1. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(fintype bigop)