Add vernacular file for subtac

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@8079 85f007b7-540e-0410-9357-904b9bb8a0f7

1 files changed, 18 insertions, 0 deletions

diff --git a/contrib/subtac/FixSub.v b/contrib/subtac/FixSub.v
new file mode 100644
index 0000000000..4279c17f57
--- /dev/null
+++ b/contrib/subtac/FixSub.v
@@ -0,0 +1,18 @@
+Require Import Coq.Init.Wf.
+
+Section FixPoint.
+
+Variable A : Set.
+Variable R : A -> A -> Prop.
+Hypothesis Rwf : well_founded R.
+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.
+