proposition: Lemma stablemxD : stablemx V f -> stablemx V g -> stablemx V (f + g).
proof: Proof. by move=> f_stab g_stab; rewrite mulmxDr addmx_sub. 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 finalg zmodp matrix)