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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _e(op, inv=False):
 """ Lightweight factory which returns a method that builds an Expression consisting of the left-hand and right-hand operands, using `op`. """

        def inner(self, rhs):
            if inv:
                return Expression(rhs, op, self)
            return Expression(self, op, rhs)
        return inner