Beyond the Turing threshold: Productive grammars generate essentially undecidable languages
A theoretical paper designs formal grammars that emulate Post's productive sets, generating languages that are provably beyond Turing decidability.
The paper elaborates on Emil Post's productive sets, which are not even semi-computable, and builds formal grammars that emulate their construction over natural numbers. The resulting languages are shown to be essentially undecidable, placing them beyond Turing decidability. This is pure computability and formal language theory with limited direct security relevance.