From 222a8d9abf3724ab2458aecf445ad21c12da902e Mon Sep 17 00:00:00 2001
From: Jason Gross <jgross@mit.edu>
Date: Wed, 10 Oct 2018 10:12:45 -0400
Subject: Add [normalize_commutative_identifier] tactic

---
 _CoqProject                                 |  1 +
 src/Util/Tactics/RewriteWithCommutativity.v | 16 ++++++++++++++++
 2 files changed, 17 insertions(+)
 create mode 100644 src/Util/Tactics/RewriteWithCommutativity.v

diff --git a/_CoqProject b/_CoqProject
index 34aaea9f7..9f814f84c 100644
--- a/_CoqProject
+++ b/_CoqProject
@@ -6591,6 +6591,7 @@ src/Util/Tactics/PoseTermWithName.v
 src/Util/Tactics/PrintContext.v
 src/Util/Tactics/Revert.v
 src/Util/Tactics/RewriteHyp.v
+src/Util/Tactics/RewriteWithCommutativity.v
 src/Util/Tactics/RunTacticAsConstr.v
 src/Util/Tactics/SetEvars.v
 src/Util/Tactics/SetoidSubst.v
diff --git a/src/Util/Tactics/RewriteWithCommutativity.v b/src/Util/Tactics/RewriteWithCommutativity.v
new file mode 100644
index 000000000..00af95566
--- /dev/null
+++ b/src/Util/Tactics/RewriteWithCommutativity.v
@@ -0,0 +1,16 @@
+(** Rewrite with the commutative property to ensure that all appearences of an identifier show up the same way *)
+
+Ltac rewrite_with_comm id clem x y :=
+  first [ constr_eq x y; fail 1
+        | repeat match goal with
+                 | [ H' : context[id y x] |- _ ]
+                   => rewrite clem in H'
+                 | [ |- context[id y x] ]
+                   => rewrite clem
+                 end ].
+
+Ltac normalize_commutative_identifier id id_comm :=
+  repeat match goal with
+         | [ |- context[id ?x ?y] ] => progress rewrite_with_comm id (id_comm y x) x y
+         | [ H : context[id ?x ?y] |- _ ] => progress rewrite_with_comm id (id_comm y x) x y
+         end.
-- 
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