proposition: Lemma col_mxEd A1 A2 i j : col_mx A1 A2 (rshift m1 i) j = A2 i j.
proof: Proof. by rewrite mxE (unsplitK (inr _ _)). 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)