public void remove(lalr_item itm) throws internal_error {
  not_null(itm);
  hashcode_cache=null;
  _all.remove(itm);
}

public void remove ( lalr_item itm ) throws internal_error { not_null ( itm ) ; hashcode_cache = null ; _all . remove ( itm ) ; }
remove a single item if it is in the set .
