1. AHU74 Aho, A.V., Hopcroft, J.E., Ullman, J.D.: The design and analysis of computer algorithms. Reading, MA: Addison-Wesley 1974
2. CKS81 Chandra, A.K., Kozen, D.C., Stockmeyer, L.J.: Alternation. J. ACM28, 114?133 (1981)
3. Gin75 Ginsburg, S.: Algebraic and automata-theoretic properties of formal languages. North Holland, Amsterdam: North Holland 1975
4. HU69 Hopcroft, J.E., Ullman, J.D.: Formal languages and their relation to automata. Reading, MA: Addison-Wesley 1969
5. Hr85 Hromkovi?, J.: On the power of alternation in automata theory. J. Comput. Syst. Sci.31, 28?39 (1985)