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Period 2

 
Figure: : A four cell ring repeated four times fills a sixteen cell ring.  

Since the cycle of period two has length four, it will recur in every ring whose length is a multiple of four. Cycles of very short period can usually be deduced by ad hoc methods, but their de Bruijn diagrams are sufficiently small that they can be rapidly identified from hand drawn graphs.



Harold V. McIntosh
E-mail:mcintosh@servidor.unam.mx