proposition: Lemma mxdiagN (B_ : forall i, 'M[V]_(p_ i)) : \mxdiag_i (- B_ i) = - \mxdiag_i (B_ i).
proof: Proof. rewrite /mxdiag -mxblockN; apply/eq_mxblock => i j. by case: eqVneq => [->|]; rewrite ?conform_mx_id ?oppr0. 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)