Improve syntax for `Combinator` rules

[tasooshi]

So:

        self.left(usernames, self.bits('extra-common')),
        self.right(self.temp('extra-common+simple-brutas-usernames'), self.bits('months')),

Could be written for example as:

        usernames < self.bits('extra-common'),
        self.temp('extra-common+simple-brutas-usernames') > self.bits('months'),