Context-sensitive grammars and linear bounded automata
Context-sensitive productions replace αAβ by αγβ with γ nonempty; equivalently, their nonempty-word languages admit noncontracting productions u→v with |u|≤|v| and a nonterminal in u.
Key knowledge
Context-sensitive productions replace αAβ by αγβ with γ nonempty; equivalently, their nonempty-word languages admit noncontracting productions u→v with |u|≤|v| and a nonterminal in u. These languages are exactly those accepted by nondeterministic linear bounded automata, whose tape is confined to a constant multiple of input length.
Conditions and scope
- Here the strict grammar convention excludes ε. To include ε permit only S→ε with S absent from every right-hand side, and treat the LBA's empty input separately.
- Input/tape alphabets are finite and fixed; finitely many tape tracks or a larger alphabet absorb constant linear factors. Nondeterminism is essential to the stated equivalence and is not asserted eliminable at the same space bound.
Sources · 1
References
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Evidence and review
Slides 18 and 24–25 definitions/epsilon exception and monotonic equivalence; slides 33–38 LBA and Myhill–Landweber–Kuroda theorem with reverse-derivation and simulated-machine proof outline. The converse detailed grammar construction is summarized, not fully proved in these slides.
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