In 1966, Semenov, by using a technique based on power series, suggested an algorithm that tells apart the languages described by an unambiguous grammar and a DFA. At the first glance, it may appear that the algorithm can be easily modified to yield a full solution of the equivalence problem for unambiguous grammars. This article shows why this hunch is, in fact, incorrect.

翻译：1966年,塞梅诺夫通过使用基于电力序列的技术,提出了一个算法,将用明确的语法和DFA描述的语言区分开来。乍一看,这一算法似乎可以很容易地修改,以便为明确的语法的等同问题找到一个完整的解决办法。这篇文章说明了为什么这种直觉事实上是不正确的。