proposition: Lemma block_mxEur i j : A (lshift m2 i) (rshift n1 j) = Aur i j.
proof: Proof. by rewrite col_mxEu row_mxEr. 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)