public boolean add(terminal_set other) throws internal_error {
  not_null(other);
  BitSet copy=(BitSet)_elements.clone();
  _elements.or(other._elements);
  return !_elements.equals(copy);
}

public boolean add ( terminal_set other ) throws internal_error { not_null ( other ) ; BitSet copy = ( BitSet ) _elements . clone ( ) ; _elements . or ( other . _elements ) ; return ! _elements . equals ( copy ) ; }
add ( union ) in a complete set .
