Section Weak.
(** A `label' is either the silent action, or a visible one *)
Inductive Lbl: Type := T | L(a: A).
Definition reduction_t := reduction Lbl.
Variable X: Type.
Variable Red: reduction_t X.
(** Weak transition relation *)
Definition Weak: reduction_t X := fun l =>
match l with
| T => star (Red T)
| L a => comp (star (Red T)) (comp (Red (L a)) (star (Red T)))
end.
(** Transition relation for expansion *)
Definition EWeak: reduction_t X := fun l =>
match l with
| T => union2 (eq (A:=X)) (Red T)
| L a => Red (L a)
end.
(** Transition relation for relaxed expansion *)
Definition REWeak: reduction_t X := fun l =>
match l with
| T => union2 (eq (A:=X)) (Red T)
| L a => comp (Red (L a)) (star (Red T))
end.

(** A useful induction principle: just look at the first action *)
Theorem Weak_ind:
forall P: Lbl -> X -> X -> Prop,
(forall x, P T x x) ->
(forall y l x z ,
Red T x y -> Weak l y z -> P l y z -> P l x z) ->
(forall y a x z,
Red (L a) x y -> Weak T y z -> P T y z -> P (L a) x z) ->
forall l x x', Weak l x x' -> P l x x'.