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