def verify(self, func=None, *args, **kwargs):
        """Subtract the rhs from the lhs of the equation

        Before the substraction, each side is expanded and any scalars are
        simplified. If given, `func` with the positional arguments `args` and
        keyword-arguments `kwargs` is applied to the result before returning
        it.

        You may complete the verification by checking the :attr:`is_zero`
        attribute of the returned expression.
        """
        res = (
            self.lhs.expand().simplify_scalar() -
            self.rhs.expand().simplify_scalar())
        if func is not None:
            return func(res, *args, **kwargs)
        else:
            return res