diff -r 5eb932e604a2 -r eab6ce8368fa src/HOL/Quickcheck_Examples/Quickcheck_Examples.thy
--- a/src/HOL/Quickcheck_Examples/Quickcheck_Examples.thy	Wed Jan 10 15:21:49 2018 +0100
+++ b/src/HOL/Quickcheck_Examples/Quickcheck_Examples.thy	Wed Jan 10 15:25:09 2018 +0100
@@ -474,8 +474,8 @@
   fixes R
   assumes "R x y --> R y x --> x = y"
 
-interpretation equal : antisym "op =" by standard simp
-interpretation order_nat : antisym "op <= :: nat => _ => _" by standard simp
+interpretation equal : antisym "(=)" by standard simp
+interpretation order_nat : antisym "(<=) :: nat => _ => _" by standard simp
 
 lemma (in antisym)
   "R x y --> R y z --> R x z"