(**************************************************)
(* Reduction of a lambda term by a set of redexes *)
(**************************************************)
Definition reduction (M : lambda) (U : redexes) (N : lambda) :=
residuals (mark M) U (mark N).

(* Specifications: *)
Lemma reduction_function :
forall (M N P : lambda) (U : redexes),
reduction M U N -> reduction M U P -> N = P.