src/HOL/Orderings.thy

 print_translation {*
 let
   val All_binder = Syntax.binder_name @{const_syntax All};
   val Ex_binder = Syntax.binder_name @{const_syntax Ex};
   val impl = @{const_syntax HOL.implies};
-  val conj = @{const_syntax "op &"};
+  val conj = @{const_syntax HOL.conj};
   val less = @{const_syntax less};
   val less_eq = @{const_syntax less_eq};
 
   val trans =
    [((All_binder, impl, less),