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- Rastislav Lenhardt, Jyrki Alakuijala
- 2012 Data Compression Conference
- 2012

Gipfeli is a high-speed compression algorithm that uses backward references with a 16-bit sliding window, based on 1977 paper by Lempel and Ziv, enriched with an ad-hoc entropy coding for both literals and backward references. We have implemented it in C++ and fine-tuned for very high performance. The compression ratio is similar to Zlib in the fastest… (More)

- Michael Benedikt, Rastislav Lenhardt, James Worrell
- TACAS
- 2013

Interval Markov chains (IMCs) generalize ordinary Markov chains by having interval-valued transition probabilities. They are useful for modeling systems in which some transition probabilities depend on an unknown environment, are only approximately known, or are parameters that can be controlled. We consider the problem of computing values for the unknown… (More)

- Rastislav Lenhardt
- CONCUR
- 2011

Model checking linear-time properties expressed in first-order logic has nonelementary complexity, and thus various restricted logical languages are employed. In this paper we consider two such restricted specification logics, linear temporal logic (LTL) and two-variable first-order logic (FO). LTL is more expressive but FO can be more succinct, and hence… (More)

- Saguy Benaim, Michael Benedikt, +4 authors James Worrell
- ACM Trans. Comput. Log.
- 2013

Verification of properties expressed in the two-variable fragment of first-order logic FO<sup>2</sup> has been investigated in a number of contexts. The satisfiability problem for FO<sup>2</sup> over arbitrary structures is known to be NEXPTIME-complete, with satisfiable formulas having exponential-sized models. Over words, where FO<sup>2</sup> is known to… (More)

- Michael Benedikt, Rastislav Lenhardt, James Worrell
- ArXiv
- 2014

An automaton is unambiguous if each word has at most one accepting run and separated if no word is accepted from two distinct states. The classical translation of LTL formulas to Büchi automata [5] produces unambiguous separated automata since the states of such automata correspond to complete subformula types. Motivated by this observation, Couvreur et al.… (More)

- Saguy Benaim, Michael Benedikt, Rastislav Lenhardt, James Worrell
- ArXiv
- 2013

Verification of properties of first order logic with two variables FO has been investigated in a number of contexts. Over arbitrary structures it is known to be decidable with NEXPTIME complexity, with finitely satisfiable formulas having exponential-sized models. Over word structures, where FO is known to have the same expressiveness as unary temporal… (More)

- Michael Benedikt, Rastislav Lenhardt, James Worrell
- QEST
- 2012

- Rastislav Lenhardt
- QEST
- 2013

Probabilistic automata were introduced by Rabin in early 1960s. We extend this concept by allowing transition probabilities among the states to be parametric. Two main decision problems are considered: the language equivalence and bisimulation of probabilistic automata. One of our main results is a new one sided error Monte Carlo randomized polynomial-time… (More)

- Rastislav Lenhardt
- ArXiv
- 2010

In the last decade, the power of the state-of-the-art SAT and ILP (Integer Linear Programming) solvers has dramatically increased. They implement many new techniques and heuristics and since any NP problem can be converted to SAT or ILP instance, we could take advantage of these techniques in general by converting the instance of NP problem to SAT formula… (More)

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