Since the 1970s, the smallest known non-finitely based involution semigroups are of order six. This paper exhibits the first example of a non-finitely based involution semigroup of order five.

中文翻译：

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基于五阶的非有限对合半群

自1970年代以来，已知的最小的非有限对合半群的数量级为6。本文展示了一个五阶非有限对合半群的第一个例子。