proposition: Lemma trmx_mxsub m1 m2 n1 n2 f g (A : 'M_(m1, n1)) : (mxsub f g A)^T = mxsub g f A^T :> 'M_(n2, m2).
proof: Proof. by apply/matrixP => i j; rewrite !mxE. 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)