diff -r 352c73a689da -r c3d6e570ccef src/HOL/Finite_Set.thy
--- a/src/HOL/Finite_Set.thy	Wed Nov 04 08:13:49 2015 +0100
+++ b/src/HOL/Finite_Set.thy	Wed Nov 04 08:13:52 2015 +0100
@@ -1197,7 +1197,7 @@
   "card = folding.F (\<lambda>_. Suc) 0"
 
 interpretation card!: folding "\<lambda>_. Suc" 0
-where
+rewrites
   "folding.F (\<lambda>_. Suc) 0 = card"
 proof -
   show "folding (\<lambda>_. Suc)" by standard rule