1. Robert H. Oehmke,On Projective Automata, Pure Mathematics and Applications, Vol. 5(1992), No. 3 – 4, pp. 243–250, Budapest, Hungary.
2. C.H. Park,On right congruences associated with the input Semigroup S of Automata, Semigroup Forum Vol.48(1994) 263–271.
3. C.H. Park,On Free and Torsion-Free Automata, Pure Mathematics and Applications Ser. A, Vol. 5(1994), No.2, pp. 191–194, Budapest, Hungary.
4. C.H. Park,Small and Large Automata, Korean J. Com.and Appl. Math. Vol.2 (1995), No. 2, pp. 69–74
5. C.H. Park,Some Remarks on The Automata-Homomorphisms, Comm. Korean Math. Soc.8(1993), No. 3, pp. 799–809.