Introduction to Formal Language Theory
Introduction to Formal Language Theory
Economy of description by automata, grammars, and formal systems
SWAT '71 Proceedings of the 12th Annual Symposium on Switching and Automata Theory (swat 1971)
Complexity of multi-head finite automata: Origins and directions
Theoretical Computer Science
Descriptional complexity of two-way pushdown automata with restricted head reversals
DCFS'11 Proceedings of the 13th international conference on Descriptional complexity of formal systems
Parikh's theorem and descriptional complexity
SOFSEM'12 Proceedings of the 38th international conference on Current Trends in Theory and Practice of Computer Science
Descriptional complexity of two-way pushdown automata with restricted head reversals
Theoretical Computer Science
Some decision problems concerning NPDAs, palindromes, and dyck languages
CIAA'13 Proceedings of the 18th international conference on Implementation and Application of Automata
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Finite-turn pushdown automata (PDA) are investigated concerning their descriptional complexity. It is known that they accept exactly the class of ultralinear context-free languages. Furthermore, the increase in size when converting arbitrary PDAs accepting ultralinear languages to finite-turn PDAs cannot be bounded by any recursive function. The latter phenomenon is known as non-recursive trade-off. In this paper, finite-turn PDAs accepting letter-bounded languages are considered. It turns out that in this case the non-recursive trade-off is reduced to a recursive trade-off, more precisely, to an exponential trade-off. A conversion algorithm is presented and the optimality of the construction is shown by proving tight lower bounds. Furthermore, the question of reducing the number of turns of a given finite-turn PDA is studied. Again, a conversion algorithm is provided which shows that in this case the trade-off is at most polynomial.