1. Lecture Notes in Computer Science;L. Alfaro de,2003
2. Asarin, E., Maler, O.: Achilles and the tortoise climbing up the arithmetical hierarchy. JCSS 57(3), 389–398 (1998)
3. Lecture Notes in Computer Science;A. Bès,2005
4. Lecture Notes in Computer Science;P. Bouyer,2003
5. Bedon, N.: Langages reconnaissables de mots indexés par des ordinaux. PhD thesis, Université de Marne-la-Vallée (1998)