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src/HOL/Library/Countable.thy
changeset 37388 793618618f78
parent 35700 951974ce903e
child 37652 6aa09d2a6cf9 
--- a/src/HOL/Library/Countable.thy	Tue Jun 08 16:37:19 2010 +0200
+++ b/src/HOL/Library/Countable.thy	Tue Jun 08 16:37:22 2010 +0200
@@ -70,7 +70,7 @@
 
 text {* Sums *}
 
-instance "+":: (countable, countable) countable
+instance "+" :: (countable, countable) countable
   by (rule countable_classI [of "(\<lambda>x. case x of Inl a \<Rightarrow> to_nat (False, to_nat a)
                                      | Inr b \<Rightarrow> to_nat (True, to_nat b))"])
     (simp split: sum.split_asm)
isabelle