Section enum_red2.
Variables (X Y Z : Type) (p : X -> Prop) (q : Y -> Prop).
Variables (f : X -> Y) (Hf : forall x, p x <-> q (f x)).
Variables (g: Y -> Z) (Hg: forall y1 y2, g y1 = g y2 -> q y1 <-> q y2).
Variables (Lq : _) (qe : enum q Lq).
Variables (d : Dis Z).
Variable (LX: enumT X).
Fixpoint Lalt  n :=
match n with
| 0 => []
| S n => Lalt n ++ [ x | x ∈ L_T X n, (g (f x) ∈ map g (Lq n)) ]
end.

Lemma enum_red2:
enum p Lalt.