Let $extbf{T}(n,k)$ be the set of strings of length $n$ over the alphabet $Sigma={1,2,ldots,k}$. A universal cycle for $extbf{T}(n,k)$ can be constructed using a greedy algorithm: start with the string $k^n$, and continually append the least symbol possible without repeating a substring of length $n$. This construction also creates universal cycles for some subsets $extbf{S}subseteqextbf{T}(n,k)$; we will classify all such subsets that are closed under rotations.
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机译：让$ textbf {t}（n，k）$是字母$ n $ over字母$ sigma = {1,2， ldots，k } $。可以使用贪婪算法构建$ textbf {t}（n，k）$的通用周期：以字符串$ k ^ n $开头，并不断追加可能的最小符号，而不会重复长度$ n $的子字符串。这种施工还为某些子集合 textbf {s} subseteq textbf {t}（n，k）$;我们将分类所有在旋转下关闭的子集。
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