proposition: Lemma mul_mxblock_mxrow m (B_ : forall i j, 'M[R]_(q_ i, p_ j)) (C_ : forall i, 'M[R]_(p_ i, m)) : \mxblock_(i, j) B_ i j *m \mxcol_j C_ j = \mxcol_i (\sum_j (B_ i j *m C_ j)).
proof: Proof. rewrite mxblockEh mul_mxrow_mxcol mxcol_sum. by apply: eq_bigr => i _; rewrite mxcol_mul. 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)