Wojciech Czerwinski

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Bisimulation equivalence is decidable in polynomial time over normed graphs generated by a context-free grammar. We present a new algorithm, working in time O(n 5), thus improving the previously known complexity O(n 8 polylog(n)). It also improves the previously known complexity O(n 6 polylog(n)) of the equality problem for simple grammars. 1 Introduction(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 piecewise-and 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)
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)
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 nondeter-ministic finite automaton. The problem becomes EXPSPACE-complete if the language is(More)
The paper is about a class of languages that extends context-free languages (CFL) and is stable under shuffle. Specifically, we investigate the class of partially-commutative context-free languages (pc CFL), where non-terminal symbols are commutative according to a binary independence relation, very much like in trace theory. The class has been recently(More)
We show that any one-counter automaton with n states, if its language is non-empty, accepts some word of length at most O(n 2). This closes the gap between the previously known upper bound of O(n 3) and lower bound of Ω(n 2). More generally, we prove a tight upper bound on the length of shortest paths between arbitrary configurations in one-counter(More)
Given two families of sets F and G, the F separability problem for G asks whether for two given sets U, V ∈ G there exists a set S ∈ F, such that U is included in S and V is disjoint with S. We consider two families of sets F: modular sets S ⊆ N d , defined as unions of equivalence classes modulo some natural number n ∈ N, and unary sets. Our main result is(More)