def in_common(m1, m2, system=1):
    """Return clauses in common

    Arguments:
        m1 {MentalModel} -- model 1
        m2 {MentalModel} -- model 2

    Keyword Arguments:
        system {int} -- system 1 or 2 (default: {1})

    Raises:
        Exception: if system not 1 or 2

    Returns:
        tuple -- (clause in common, index in model 1, index in model 2)
    """
    if system == 1:
        clauses_1 = m1.clauses
        clauses_2 = m2.clauses
    elif system == 2:
        clauses_1 = m1.full_clauses
        clauses_2 = m2.full_clauses
    else:
        raise Exception
    return [
        (cl1, i1, i2)
        for i1, cl1 in enumerate(clauses_1)
        for i2, cl2 in enumerate(clauses_2)
        if cl1 == cl2]