src/Pure/type.ML

   val could_unifys: typ list * typ list -> bool
   val eq_type: tyenv -> typ * typ -> bool
 
   (*extend and merge type signatures*)
   val add_class: Pretty.pp -> NameSpace.naming -> bstring * class list -> tsig -> tsig
-  val hide_classes: bool -> string list -> tsig -> tsig
+  val hide_class: bool -> string -> tsig -> tsig
   val set_defsort: sort -> tsig -> tsig
   val add_types: NameSpace.naming -> (bstring * int) list -> tsig -> tsig
   val add_abbrevs: NameSpace.naming -> (string * string list * typ) list -> tsig -> tsig
   val add_nonterminals: NameSpace.naming -> string list -> tsig -> tsig
-  val hide_types: bool -> string list -> tsig -> tsig
+  val hide_type: bool -> string -> tsig -> tsig
   val add_arity: Pretty.pp -> arity -> tsig -> tsig
   val add_classrel: Pretty.pp -> class * class -> tsig -> tsig
   val merge_tsigs: Pretty.pp -> tsig * tsig -> tsig
 end;
 

         handle TYPE (msg, _, _) => error msg;
       val space' = space |> NameSpace.declare naming c';
       val classes' = classes |> Sorts.add_class pp (c', cs');
     in ((space', classes'), default, types) end);
 
-fun hide_classes fully cs = map_tsig (fn ((space, classes), default, types) =>
-  ((fold (NameSpace.hide fully) cs space, classes), default, types));
+fun hide_class fully c = map_tsig (fn ((space, classes), default, types) =>
+  ((NameSpace.hide fully c space, classes), default, types));
 
 
 (* arities *)
 
 fun add_arity pp (t, Ss, S) tsig = tsig |> map_tsig (fn ((space, classes), default, types) =>

   NameSpace.merge_tables (Library.eq_snd (op = : serial * serial -> bool)) (types1, types2)
     handle Symtab.DUP d => err_in_decls d (the_decl types1 d) (the_decl types2 d);
 
 end;
 
-fun hide_types fully cs = map_tsig (fn (classes, default, (space, types)) =>
-  (classes, default, (fold (NameSpace.hide fully) cs space, types)));
+fun hide_type fully c = map_tsig (fn (classes, default, (space, types)) =>
+  (classes, default, (NameSpace.hide fully c space, types)));
 
 
 (* merge type signatures *)
 
 fun merge_tsigs pp (tsig1, tsig2) =