On the decidability of accessibility problems (extended abstract)
STOC '00 Proceedings of the thirty-second annual ACM symposium on Theory of computing
Leftist Grammars and the Chomsky Hierarchy
Theory of Computing Systems
On complexity of grammars related to the safety problem
Theoretical Computer Science
The Ordinal Recursive Complexity of Lossy Channel Systems
LICS '08 Proceedings of the 2008 23rd Annual IEEE Symposium on Logic in Computer Science
Leftist Grammars Are Non-primitive Recursive
ICALP '08 Proceedings of the 35th international colloquium on Automata, Languages and Programming, Part II
Post embedding problem is not primitive recursive, with applications to channel systems
FSTTCS'07 Proceedings of the 27th international conference on Foundations of software technology and theoretical computer science
The ω-regular post embedding problem
FOSSACS'08/ETAPS'08 Proceedings of the Theory and practice of software, 11th international conference on Foundations of software science and computational structures
Pumping and counting on the regular post embedding problem
ICALP'10 Proceedings of the 37th international colloquium conference on Automata, languages and programming: Part II
Computing blocker sets for the regular post embedding problem
DLT'10 Proceedings of the 14th international conference on Developments in language theory
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Leftist grammars [Motwani et al., STOC 2000] are special semi-Thue systems where symbols can only insert or erase to their left. We develop a theory of leftist grammars seen as word transformers as a tool toward rigorous analyses of their computational power. Our main contributions in this first paper are (1) constructions proving that leftist transformations are closed under compositions and transitive closures, and (2) a proof that bounded reachability is NP-complete even for leftist grammars with acyclic rules.