proposition: Lemma fscomp_inj g f : injective f -> injective g -> injective (g \o f)%fsfun.
proof: Proof. by move=> f_inj g_inj k k'; rewrite !fscompE => /= /g_inj /f_inj. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)