proposition: Lemma actmE a : a \in D -> actm to a =1 to^~ a.
proof: Proof. by move=> Da; rewrite actmEfun. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(fintype bigop finset fingroup morphism perm) mathcomp(automorphism quotient)