SWhat changed
Immerman and Szelepcsényi independently established that nondeterministic space at least logarithmic in input length is closed under complement, including NL = co-NL and complement closure of context-sensitive languages.
Scientific scope
Immerman and Szelepcsényi independently established that nondeterministic space at least logarithmic in input length is closed under complement, including NL = co-NL and complement closure of context-sensitive languages. The theorem concerns nondeterministic space at least logarithmic under the stated machine/space conventions, including NL=coNL. It does not imply NP=coNP or L=NL. Verified reachable counts and finite configuration encoding are essential; flipping nondeterministic outcomes is unsound. Independent Szelepcsényi credit is source-supported, but his complete proof has not been independently reconstructed here.
Evidence
Source-linked, scoped account of the original work. The published scope states the scientific assumptions and remaining verification limits. WRS has not independently certified the full proof, experimental result or system benchmark.
Contributors
- Neil Immerman · SCIENCE: Original source-listed scientific author of this scoped work; byline does not determine effort fractions.
- Róbert Szelepcsényi · SCIENCE: Original source-listed scientific author of this scoped work; byline does not determine effort fractions.
- Immerman: Nondeterministic Space is Closed Under Complementation — author version
- Immerman — 1988 SIAM publisher metadata
- Szelepcsényi — 1988 Acta Informatica publisher identity and abstract
- ACM-SIGACT: original 1995 Gödel Prize independent-proof citation
Provisional WRS assessment, edition 2026-10-16.1. Independent expert calibration is pending. This grade does not certify correctness or assign ownership.
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