Section kHomExtend.
Variables (K E : {subfield L}) (f : 'End(L)) (x y : L).
Fact kHomExtend_subproof :
linear (fun z => (map_poly f (Fadjoin_poly E x z)).[y]).
Definition kHomExtend := linfun (Linear kHomExtend_subproof).
End kHomExtend.
Definition kAut U V f := kHom U V f && (f @: V == V)%VS.

Lemma kAutS U1 U2 V f : (U1 <= U2)%VS -> kAut U2 V f -> kAut U1 V f.