src/Pure/Isar/token.ML

   val is_command: T -> bool
   val keyword_with: (string -> bool) -> T -> bool
   val is_command_modifier: T -> bool
   val ident_with: (string -> bool) -> T -> bool
   val is_proper: T -> bool
-  val is_improper: T -> bool
   val is_comment: T -> bool
   val is_informal_comment: T -> bool
   val is_formal_comment: T -> bool
   val is_ignored: T -> bool
   val is_begin_ignore: T -> bool

 
 fun is_proper (Token (_, (Space, _), _)) = false
   | is_proper (Token (_, (Comment _, _), _)) = false
   | is_proper _ = true;
 
-val is_improper = not o is_proper;
-
 fun is_comment (Token (_, (Comment _, _), _)) = true
   | is_comment _ = false;
 
 fun is_informal_comment (Token (_, (Comment NONE, _), _)) = true
   | is_informal_comment _ = false;