Section OpsTheory.
Variable T : finType.
Implicit Types (A B C D: {pred T}) (P Q : pred T) (x y : T) (s : seq T).
Variant pick_spec : option T -> Type :=
| Pick x of P x         : pick_spec (Some x)
| Nopick of P =1 xpred0 : pick_spec None.
End EnumPick.
Hint Resolve subxx_hint : core.
Definition iinv A y fAy := s2val (@iinv_proof A y fAy).

Lemma bij_on_image A (x0 : T) : {on [pred y in image f A], bijective f}.