Immerman–Szelepcsényi theorem

The Immerman–Szelepcsényi theorem is a result in computational complexity theory that establishes a relationship between two significant complexity classes: **NL** (nondeterministic logarithmic space) and **co-NL** (the complement of NL). Specifically, the theorem proves that these two classes are equal, i.e., \[ \text{NL} = \text{co-NL}.