def not_(self, other):
        """Negate a ternary value.

        (Python doesn't allow useful overriding of ``not``.)

        """
        if other is self:
            return other
        elif other is True:
            return False
        elif other <= False:
            return True
        else:
            raise TypeError(type(other).__name__)
dataset/ETHPy150Open jek/flatland/flatland/util/base.py/Maybe.not_/operator `is` -> `<=`