errors in gb_sets and gn_trees

[Kostis Sagonas]

Modules gb_sets and gb_trees each define an insert/2 function whose 
documentation (for gb_sets) reads:

   insert(Element, Set1) -> Set2
      Types:
        Element = term()
        Set1 = Set2 = gb_set()
   Returns a new gb_set formed from Set1 with Element inserted. Assumes
   that Element is not present in Set1.

and whose code reads:

   insert(Key, Val, {S, T}) when is_integer(S) ->
     S1 = S+1,
     {S1, insert_1(Key, Val, T, ?pow(S1, ?p))}.

   insert_1(Key, Value, {Key1, V, Smaller, Bigger}, S) when Key < Key1 ->
     case insert_1(Key, Value, Smaller, ?div2(S)) of
   ....
   insert_1(Key, _, _, _) ->
     erlang:error({key_exists, Key}).

Should the last line be a call to erlang:error/1 or to erlang:throw/1 ?

Kostis