From 14f8db195021e709734ed89d9cb513d1c0db6a93 Mon Sep 17 00:00:00 2001
From: Hugo Herbelin
Date: Mon, 3 Oct 2016 22:12:56 +0200
Subject: Fixing #4970 (confusion between special "{" and non special "{{" in
 notations).

---
 test-suite/bugs/closed/4970.v | 3 +++
 toplevel/metasyntax.ml        | 5 ++++-
 2 files changed, 7 insertions(+), 1 deletion(-)
 create mode 100644 test-suite/bugs/closed/4970.v

diff --git a/test-suite/bugs/closed/4970.v b/test-suite/bugs/closed/4970.v
new file mode 100644
index 0000000000..7a896582f5
--- /dev/null
+++ b/test-suite/bugs/closed/4970.v
@@ -0,0 +1,3 @@
+(* Check "{{" is not confused with "{" in notations *)
+Reserved Notation "x {{ y }}" (at level 40).
+Notation "x {{ y }}" := (x y) (only parsing).
diff --git a/toplevel/metasyntax.ml b/toplevel/metasyntax.ml
index 92208e3046..4f41043e87 100644
--- a/toplevel/metasyntax.ml
+++ b/toplevel/metasyntax.ml
@@ -1203,7 +1203,10 @@ let contract_notation ntn =
   let rec aux ntn i =
     if i <= String.length ntn - 5 then
       let ntn' =
-        if String.is_sub "{ _ }" ntn i then
+        if String.is_sub "{ _ }" ntn i &&
+           (i = 0 || ntn.[i-1] = ' ') &&
+           (i = String.length ntn - 5 || ntn.[i+5] = ' ')
+        then
           String.sub ntn 0 i ^ "_" ^
           String.sub ntn (i+5) (String.length ntn -i-5)
         else ntn in
-- 
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