1. An nlogn algorithm for minimizing states in a finite automaton;Hopcroft,1971
2. The equivalence problem for regular expressions with squaring requires exponential space;Meyer,1972
3. Minimizing nfas and regular expressions;Gramlich,2005
4. Minimizing nfa’s and regular expressions;Gramlich;Journal of Computer and System Sciences,2007
5. Inapproximability of nondeterministic state and transition complexity assuming P≠NP;Gruber,2007