proposition: Lemma map2_usubmx : map2_mx (usubmx Bv) (usubmx B'v) = usubmx (map2_mx Bv B'v).
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)