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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 subtract(self, expr, simplify):
 """ Return a new expression where the `expr` expression has been removed from this expression if it exists. """

        args = self.args
        if expr in self.args:
            args = list(self.args)
            args.remove(expr)
        elif isinstance(expr, self.__class__):
            if all(arg in self.args for arg in expr.args):
                args = tuple(arg for arg in self.args if arg not in expr)
        if len(args) == 0:
            return None
        if len(args) == 1:
            return args[0]

        newexpr = self.__class__(*args)
        if simplify:
            newexpr = newexpr.simplify()
        return newexpr