proposition: Lemma memv_gal E (x : gal_of E) a : a \in E -> x a \in E.
proof: Proof. by move/(memv_img x); rewrite limg_gal. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype tuple finfun bigop ssralg poly) mathcomp(polydiv finset fingroup morphism quotient perm) mathcomp(action zmodp cyclic matrix mxalgebra vector) mathcomp(falgebra fieldext separable)