@property<EOL><INDENT>def next_unit_id(self) -> int:<DEDENT>
ids: typing.Set[int] = set()<EOL>for unit in chain(self._blue_coa.units, self._red_coa.units):  <EOL><INDENT>id_ = unit.unit_id<EOL>if id_ in ids:<EOL><INDENT>raise IndexError(unit.unit_name)<EOL><DEDENT>ids.add(id_)<EOL><DEDENT>return max(ids) + <NUM_LIT:1><EOL>
Returns: next free Unit ID