Canonical subvs_fieldType K :=
Eval hnf in FieldType (subvs_of K) (@subvs_fieldMixin K).
Canonical subvs_fieldExtType K := Eval hnf in [fieldExtType F0 of subvs_of K].

Lemma gcdp_polyOver K :
{in polyOver K &, forall p q, gcdp p q \is a polyOver K}.