Section APD.
Variable X V R : Ensf.
Variable S' : Elt.
Hypothesis Gram : isGram X V R S'.
apply isGram4 with S'.
exact Gram.
Qed.
Let P := union X V.
Let f_R_d (a : Elt) :=
couple (word (cons (first a) nil)) (couple (eps X) (second a)).
Let f_X_d (x : Elt) := couple (word (cons x nil)) (couple x (word nil)).
Let d := union (map f_R_d R) (map f_X_d X).
Let wd := cons S' nil.
Let wa := nil.
red in |- *.
intros x dans_x_d.
elimtype (dans x (map f_R_d R) \/ dans x (map f_X_d X)).
intros dans_x.
elimtype (exists y : Elt, dans y R /\ x = f_R_d y).
intros y temp; elim temp; clear temp.
unfold f_R_d in |- *.
intros dans_y_R eg_x_f_y.
exists (cons (first y) nil).
apply inmonoid_cons.
trivial.
elim (Regles_X_V_R y dans_y_R).
intros f_y dans_f_y_V temp; elim temp; clear temp.
intros u eg_y inmono_u.
rewrite eg_y.
unfold first in |- *.
unfold P in |- *.
auto.
exists (eps X).
auto.
exists (word_inv (second y)).
elim (Regles_X_V_R y dans_y_R).
intros f_y dans_f_y_V temp; elim temp; clear temp.
intros u eg_y inmono_u.
rewrite eg_y.
unfold second in |- *.
unfold word_inv in |- *.
assumption.
elim (Regles_X_V_R y dans_y_R).
intros f_y dans_f_y_V temp; elim temp; clear temp.
intros u eg_y inmono_u.
replace (word (word_inv (second y))) with (second y).
assumption.
replace (second y) with (word u).
apply refl_equal.
rewrite eg_y.
apply refl_equal.
apply dans_map.
assumption.
intros dans_x.
elimtype (exists y : Elt, dans y X /\ x = f_X_d y).
intros y temp; elim temp; clear temp.
unfold f_X_d in |- *.
intros dans_y_X eg_x_f_y.
exists (cons y nil).
apply inmonoid_cons.
trivial.
unfold P in |- *.
auto.
exists y.
auto.
exists nil.
trivial.
assumption.
apply dans_map.
assumption.
auto.
Qed.
red in |- *.
split.
unfold wd in |- *.
apply inmonoid_cons.
trivial.
unfold P in |- *.
apply union_d.
apply isGram3 with X R.
exact Gram.
split.
apply inmonoid_nil.
exact Trans.
Qed.

Lemma cut_spec :
forall u : Word,
{a : Word &
{b : Word |
inmonoid X a /\
Append a b = u /\
(b = nil \/
ex2 (fun x : Elt => ~ dans x X)
(fun x : Elt => exists w : Word, b = cons x w))}}.