def configs_conflict(a, b):
    """Given two configurations, determine whether they overlap (i.e., have
    nonzero parameters for at least one site in common).
    """
    a_dict = dict(a)
    b_dict = dict(b)
    assert a_dict.keys() == b_dict.keys()

    for ident, a_param in a_dict.items():
        if a_param and b_dict[ident]:
            return True
    return False