Conway showed that the equational theory of regular expressions admit models in which a* was not the reflexive transitive closure of a, by giving a four-element model 0 ≤ 1 ≤ a ≤ a* in which a•a = a.
Conway 证明了正则表达式的等式理论允许其中 a* 不是 a 的自反传递闭包的模型，通过给出一个四元素模型 0 ≤ 1 ≤ a ≤ a* 其中 a·a = a。