From a1daae8800194166662c87e11a974a6ae3d24a4d Mon Sep 17 00:00:00 2001
From: Jasper Hugunin
Date: Fri, 27 Nov 2020 09:26:20 -0800
Subject: A small fix for freshness in the `change` tactic

---
 tactics/eqdecide.ml                | 4 ++--
 test-suite/bugs/closed/bug_13493.v | 7 +++++++
 2 files changed, 9 insertions(+), 2 deletions(-)
 create mode 100644 test-suite/bugs/closed/bug_13493.v

diff --git a/tactics/eqdecide.ml b/tactics/eqdecide.ml
index d4cc193eb3..9b3f9053cd 100644
--- a/tactics/eqdecide.ml
+++ b/tactics/eqdecide.ml
@@ -123,8 +123,8 @@ let idy = Id.of_string "y"
 
 let mkGenDecideEqGoal rectype ops g =
   let hypnames = pf_ids_set_of_hyps g in
-  let xname    = next_ident_away idx hypnames
-  and yname    = next_ident_away idy hypnames in
+  let xname    = next_ident_away idx hypnames in
+  let yname    = next_ident_away idy (Id.Set.add xname hypnames) in
   (mkNamedProd (make_annot xname Sorts.Relevant) rectype
      (mkNamedProd (make_annot yname Sorts.Relevant) rectype
         (mkDecideEqGoal true ops
diff --git a/test-suite/bugs/closed/bug_13493.v b/test-suite/bugs/closed/bug_13493.v
new file mode 100644
index 0000000000..779df8e7f2
--- /dev/null
+++ b/test-suite/bugs/closed/bug_13493.v
@@ -0,0 +1,7 @@
+Set Mangle Names.
+
+Goal forall (m n:nat), True.
+  intros m n. compare m n.
+  - constructor.
+  - constructor.
+Qed.
-- 
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