A number of results about deterministic languages (languages accepted by pushdown automata with no choice of moves) are established. In particular, o (1) each deterministic language is unambiguous. (2) the complement of each deterministic language is a deterministic language. (3) numerous operations which preserve deterministic languages (for example, intersection with a regular set) are obtained. (4) several problems are shown to be recursively unsolvable.

Deterministic context free languages

Scattered context grammars are defined and the closure properties of the family of languages generated are considered. This family of languages is contained in the family of context sensitive languages and contains all languages accepted by linear time nondeterministic Turing machines.

Scattered context grammars.

Scattered context grammars

L(A) = L(B) ? decidability results from complete formal systems

Multitape Turing machines which can use their storage tapes only as counters or as pushdown stores are investigated. The memory access restrictions are produced by regarding the machines as small computers (as in the formalism of Wang) and by restricting the instruction repertoires. Relationships are given linking machines which only accept or reject inputs and machines which emit output sequences as a function of their input. It is shown that without restrictions on computing time or amount of tape used that only six distinct classes of sets of strings (languages) are produced by the above memory access restrictions.

Leonard Harold Haines

Papers

Generation and recognition of formal languages