proposition: Lemma astab1P x a : reflect (to x a = x) (a \in 'C[x | to]).
proof: Proof. by rewrite !inE sub1set inE; apply: eqP. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(fintype bigop finset fingroup morphism perm) mathcomp(automorphism quotient)