def eat_subphrase
    phrase = [:and, eat_expr]
    while eat_word("and"); phrase << eat_expr end
    phrase.length == 2 ? phrase[1] : phrase
  end
def eat_subphrase
    phrase = [:and, eat_expr]
    while eat_word("and"); phrase << eat_expr end
    phrase.length == 2 ? phrase[1] : phrase
  end
AND level