1. Time-varying sequential machines;Gill;J.Franklin Institute,1963
2. On the connectivity of the periodic sum of automata;Grzymała-Busse,1973
3. On the periodic sum and extensions of finite automata;Grzymała-Busse,1974
4. Algebraic structer Theory of Sequential Machines;Hartmanis,1966
5. On the connectivity of the periodic sum of finite automata;Miądowicz;Foundations of Control Engineering,1976