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diff --git a/contrib/subtac/FixSub.v b/contrib/subtac/FixSub.v
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+Require Import Wf.
+
+Section Well_founded.
+Variable A : Set.
+Variable R : A -> A -> Prop.
+Hypothesis Rwf : well_founded R.
+
+Section FixPoint.
+
+Variable P : A -> Set.
+
+Variable F_sub : forall x:A, (forall y: { y : A | R y x }, P (proj1_sig y)) -> P x.
+ 
+Fixpoint Fix_F_sub (x : A) (r : Acc R x) {struct r} : P x :=
+   F_sub x (fun y: { y : A | R y x}  => Fix_F_sub (proj1_sig y) 
+   (Acc_inv r (proj1_sig y) (proj2_sig y))).
+
+Definition Fix_sub (x : A) := Fix_F_sub x (Rwf x).
+
+End FixPoint.
+
+End Well_founded.