Definition image_mem T T' f mA : seq T' := map f (@enum_mem T mA).Notation image f A := (image_mem f (mem A)).Notation "[ 'seq' F | x : T 'in' A ]" := (image (fun x : T => F) A)
  (at level 0, F at level 99, x ident, only parsing) : seq_scope.Definition codom T T' f := @image_mem T T' f (mem T).

Lemma codomE : codom f = map f (enum T).