diff -r f075640b8868 -r 3abf6a722518 src/HOL/ZF/HOLZF.thy
--- a/src/HOL/ZF/HOLZF.thy	Tue Jan 16 09:12:16 2018 +0100
+++ b/src/HOL/ZF/HOLZF.thy	Tue Jan 16 09:30:00 2018 +0100
@@ -188,7 +188,7 @@
 definition Field :: "ZF \<Rightarrow> ZF" where
   "Field A == union (Domain A) (Range A)"
 
-definition app :: "ZF \<Rightarrow> ZF => ZF" (infixl "\<acute>" 90) \<comment>\<open>function application\<close> where
+definition app :: "ZF \<Rightarrow> ZF => ZF" (infixl "\<acute>" 90) \<comment> \<open>function application\<close> where
   "f \<acute> x == (THE y. Elem (Opair x y) f)"
 
 definition isFun :: "ZF \<Rightarrow> bool" where