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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 eval( self, expression: z3.ExprRef, model_completion: bool = False ) -> Union[None, z3.ExprRef]: """ Evaluate the expression using this model :param expression: The expression to evaluate :param model_completion: Use the default value if the model has no interpretation of the given expression :return: The evaluated expression """

        for internal_model in self.raw:
            is_last_model = self.raw.index(internal_model) == len(self.raw) - 1
            is_relevant_model = expression.decl() in list(internal_model.decls())
            if is_relevant_model or is_last_model:
                return internal_model.eval(expression, model_completion)
        return None