def tt_entails(kb, alpha):
    """Does kb entail the sentence alpha? Use truth tables. For propositional
    kb's and sentences. [Fig. 7.10]
    >>> tt_entails(expr('P & Q'), expr('Q'))
    True
    """
    assert not variables(alpha)
    return tt_check_all(kb, alpha, prop_symbols(kb & alpha), {})
Does kb entail the sentence alpha? Use truth tables. For propositional
    kb's and sentences. [Fig. 7.10]
    >>> tt_entails(expr('P & Q'), expr('Q'))
    True