Here are the Vesta SDL's reserved identifiers; they should not be redefined:
_append _assert _bind1 _defined _div _elem _find _findr _fingerprint _head _is_binding _is_bool _is_closure _is_err _is_int _is_list _is_text _length _list1 _lookup _map _max _min _mod _model_name _n _par_map _print _run_tool _same_type _self _sub _tail _type_of _v