proposition: Lemma trmx_mul A B : (A *m B)^T = B^T *m A^T.
proof: Proof. rewrite trmx_mul_rev; apply/matrixP=> k i; rewrite !mxE. by apply: eq_bigr => j _; rewrite mulrC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype finfun bigop finset fingroup perm order) mathcomp(div prime binomial ssralg countalg finalg zmodp)