Prenex Implicits codom iinv.
Arguments imageP {T T' f A y}.
Arguments codomP {T T' f y}.

(* Specifications: *)
Lemma flatten_imageP (aT : finType) (rT : eqType) A (P : pred aT) (y : rT) :
reflect (exists2 x, x \in P & y \in A x) (y \in flatten [seq A x | x in P]).