proposition: Lemma col_mxdiag (B_ : forall i, 'M[V]_(p_ i)) k : let B'_ i := if sig1 k == i then conform_mx 0 (B_ i) else 0 in col k (\mxdiag_ i B_ i) = col (sig2 k) (\mxcol_i B'_ i).
proof: Proof. by rewrite /= col_mxblock col_mxcol; apply/eq_mxcol => i; rewrite eq_sym. 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)