Wojciech Czerwinski

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We investigate the complexity of deciding whether a given regular language can be defined with a deterministic regular expression. Our main technical result shows that the problem is PSPACE-complete if the input language is represented as a regular expression or nondeterministic finite automaton. The problem becomes EXPSPACE-complete if the language is(More)
We investigate normed commutative context-free processes (Basic Parallel Processes). We show that branching bisimilarity admits the bounded response property: in the Bisimulation Game, Duplicator always has a response leading to a process of size linearly bounded with respect to the Spoiler’s process. The linear bound is effective, which leads to(More)
Bisimulation equivalence is decidable in polynomial time for both sequential and commutative normed context-free processes, known as BPA and BPP, respectively. Despite apparent similarity between the two classes, different techniques were used in each case. We provide one polynomial-time algorithm that works in a superclass of both normed BPA and BPP. It is(More)
When can two regular word languages K and L be separated by a simple language? We investigate this question and consider separation by piecewiseand suffix-testable languages and variants thereof. We give characterizations of when two languages can be separated and present an overview of when these problems can be decided in polynomial time if K and L are(More)
Tree pattern queries are being investigated in database theory for more than a decade. They are a fundamental and flexible query mechanism and have been considered in the context of querying tree structured as well as graph structured data. We revisit their containment, validity, and satisfiability problem, both with and without schema information. We(More)
This thesis is about an extension of context-free grammars with partial commutation on nonterminal symbols. In particular, we investigate the subclass with transitive dependence relation and the corresponding automaton model: stateless multi-pushdown automata. The results of the thesis are divided into three chapters. The first chapter investigates language(More)
The separability problem for languages from a class C by languages of a class S asks, for two given word languages I and E from C, whether there exists a language S from S which includes I and excludes E, that is, I ⊆ S and S ∩ E = ∅. It is known that separability for context-free languages by any class containing all definite languages (such as regular(More)
This paper is about reachability analysis in a restricted subclass of multi-pushdown automata: we assume that the control states of an automaton are partially ordered, and all transitions of an automaton go downwards with respect to the order. We prove decidability of the reachability problem, and computability of the backward reachability set. As the main(More)