Juhani Karhumäki Arto Lepistö Wojciech Plandowski Locally Periodic Versus Globally Periodic Infinite Words. 250-264 2002 100 J. Comb. Theory, Ser. A 2 http://dx.doi.org/10.1006/jcta.2002.3292 db/journals/jct/jcta100.html#KarhumakiLP02