_sources.insert (_sources.end(), _out->sources().begin(), _out->sources().end());
_master_sources = _in->master_sources();
_master_sources.insert(_master_sources.end(), _out->master_sources().begin(), _out->master_sources().end());
_sources.insert (_sources.end(), _out->sources().begin(), _out->sources().end());
_master_sources = _in->master_sources();
_master_sources.insert(_master_sources.end(), _out->master_sources().begin(), _out->master_sources().end());