proposition: Lemma mxblock_recl {p q : nat} {p_ : 'I_p -> nat} {q_ : 'I_q.+1 -> nat} (B_ : forall i j, 'M[T]_(p_ i, q_ j)) : \mxblock_(i, j) B_ i j = castmx (erefl, mxsize_recl) (row_mx (\mxcol_i B_ i ord0) (\mxblock_(i, j) B_ i (l0 j))).
proof: Proof. by rewrite !mxblockEh mxrow_recl. 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)