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The author indicates some things that need clarifying in the paper cited in the title. The paper does not make it clear that a class of objects is not equivalent to a set of tuples. In a set of tuples two different tuples cannot contain the same data. Two different objects in a given class can contain the same data. In most of the paper this does not matter. However, the simulation function between a subclass and a superclass must be injective, but the (overloaded) simulation function between the sets of tuples usually cannot be injective.