1. Codes and Automata;Berstel,2009
2. If a D0L language is k-power free then it is circular;Mignosi,1993
3. An algorithm to test if a given circular HDOL-language avoids a pattern;Cassaigne,1994
4. Bispecial factors in circular non-pushy D0L languages;Klouda;Theoret. Comput. Sci.,2012