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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)

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)

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)

Branching bisimilarity on normed BPA processes was recently shown to be decidable by Yuxi Fu (ICALP 2013) but his proof has not provided any upper complexity bound. We present a simpler approach based on relative prime decompositions that leads to a non-deterministic exponential-time algorithm; this is close to the known exponential-time lower bound.

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)

We investigate minimization of tree pattern queries that use the child relation, descendant relation, node labels, and wildcards. We prove that minimization for such tree patterns is Sigma2P-complete and thus solve a problem first attacked by Flesca, Furfaro, and Masciari in 2003. We first provide an example that shows that tree patterns cannot be minimized… (More)