diff -r 97c06cfd31e5 -r 31f2105521ee src/HOL/TLA/Memory/MemoryImplementation.thy
--- a/src/HOL/TLA/Memory/MemoryImplementation.thy	Sun Dec 27 16:40:09 2015 +0100
+++ b/src/HOL/TLA/Memory/MemoryImplementation.thy	Sun Dec 27 17:16:21 2015 +0100
@@ -33,15 +33,15 @@
 definition
   (* auxiliary predicates *)
   MVOKBARF      :: "Vals \<Rightarrow> bool"
-  where "MVOKBARF v <-> (v : MemVal) | (v = OK) | (v = BadArg) | (v = RPCFailure)"
+  where "MVOKBARF v \<longleftrightarrow> (v : MemVal) | (v = OK) | (v = BadArg) | (v = RPCFailure)"
 
 definition
   MVOKBA        :: "Vals \<Rightarrow> bool"
-  where "MVOKBA v <-> (v : MemVal) | (v = OK) | (v = BadArg)"
+  where "MVOKBA v \<longleftrightarrow> (v : MemVal) | (v = OK) | (v = BadArg)"
 
 definition
   MVNROKBA      :: "Vals \<Rightarrow> bool"
-  where "MVNROKBA v <-> (v : MemVal) | (v = NotAResult) | (v = OK) | (v = BadArg)"
+  where "MVNROKBA v \<longleftrightarrow> (v : MemVal) | (v = NotAResult) | (v = OK) | (v = BadArg)"
 
 definition
   (* tuples of state functions changed by the various components *)