- The complement of a language L, denoted L, is the set of strings not in L.
- For a complexity class C, we define co-C as the set of languages L for L in C.
- My writeup of Immerman-Szelepcsényi
- Nondeterministic Space is Closed under Complementation by Neil Immerman
- The method of forced enumeration for nondeterministic automata by Róbert Szelepcsényi