def is_abstraction(spc_dct):
    """ Check if a PES consists of a single abstraction reaction.
    """
    _abstraction = False

    ts_names = tuple(name for name in spc_dct.keys() if 'ts_' in name)
    if len(ts_names) == 1:
        ts_dct = spc_dct[ts_names[0]]
        if 'abstraction' in ts_dct['zrxn'].class_:
            _abstraction = True

    return _abstraction