Weekly research seminar
Organizers
 prof. dr hab. Mikołaj Bojańczyk
 prof. dr hab. Damian Niwiński
Information
Wednesdays, 2:15 p.m. , room: 5050Research fields
List of talks

March 21, 2007, 2:15 p.m.
Filip Murlak (Uniwersytet Warszawski)
Temporal Logics and Model Checking for Fairly Correct Systems
I will present recent results on model checking for fairly correct systems (D. Varacca, H. Voelzer, LICS'06). A fair variant of a specfication is obtained by replacing "for all paths" by "for a large set …

March 14, 2007, 2:15 p.m.
Pawel Parys (Uniwersytet Warszawski)
On Systems of Equations Satisfied in All Commutative Finite Semigroups
I show the algorithmic procedure for solving the problem: check if a system of equations has a solution in every commutative finite semigroup.

Feb. 28, 2007, 2:15 p.m.
Mikołaj Bojańczyk (Uniwersytet Warszawski)
A paradox for CTL
The property "every path belongs to (ab)*a(ab)*" can be expressed in CTL; but necessarily using existential modalities. This shows that ACTL;does not capture the common fragment of CTL and LTL.

Jan. 3, 2007, 2:15 p.m.
Maria Fraczak (Uniwersytet Warszawski)
Defining rational functions by deterministic pushdown transducers
Rational functions are partial functions from words to words. They are implemented by finite state automata extended to produce output; only some of them can be realized by deterministic pushdown transducers (deterministic pushdown automata producing …

Dec. 20, 2006, 2:15 p.m.
Sławomir Lasota (Uniwersytet Warszawski)
Bisimulation equivalence and commutative contextfree grammars
The topic will be the class of processes (transition systems) generated from the commutative contextfree grammars. I will present a method enabling to prove decidability (and to compute the complexity) of different variants of bisimulation …

Nov. 29, 2006, 2:15 p.m.
Mikołaj Bojańczyk (Uniwersytet Warszawski)
Twoway temporal logic over unranked trees
I will talk about languages of unranked trees that can be defined in a temporal logic with two operators: exists some ancestor, and exists some descendant. The point is to have an algorithm, which decides …

Nov. 23, 2006, 2:15 p.m.
Marcin Jurdziński (Uniwersytet Warszawski)
Subexponential algorithms for solving parity games
Solving parity games is polynomial time equivalent to the modal mucalculus model checking problem and its exact computational complexity is an intriguing open problem: it is known to be in UP (unambiguous NP) and coUP, …

Nov. 15, 2006, 2:15 p.m.
Filip Murlak (Uniwersytet Warszawski)
Weak automata and Wadge hierarchy
I will show a new lower bound for the height of the Wadge hierarchy of weak tree languages, i. e., the languages of infinite trees recognizable with weak automata. To this end I will prove …

Oct. 25, 2006, 2:15 p.m.
Jacek Jurewicz (Uniwersytet Warszawski)
Panic automata
Panic automata are an extension of secondorder pushdown automata (that operate on a secondorder pushdown store, ie. a stack of stacks) by the destructive "panic" operation introduced by P. Urzyczyn in order to fully relate …

Oct. 11, 2006, 2:15 p.m.
Eryk Kopczynski (Uniwersytet Warszawski)
Halfpositionally determined winning conditions
Basic definitions: games, halfpositional determinacy.  Halfpositional winning conditions and omegaregular languages. How to check whether the given omegaregular winning condition is finitely halfpositional?  Positional/suspendable conditions (PS). Definitions and examples. Halfpositional determinacy of a …


June 7, 2006, 2:15 p.m.
Sibylle Froeschle
The computational dichotomy of trueconcurrency
In concurrency theory there is a divide between the interleaving approach, in which concurrency is reduced to nondeterministic sequentialization, and the trulyconcurrent approach, which represents concurrency in a more faithful way. In this talk I …

May 31, 2006, 2:15 p.m.
Piotr Hoffman (Uniwersytet Warszawski)
Word problems
The talk will be an introduction to the world of word problems, in particular word problems for varieties of semigroups. Attention will be paid especially to commutative semigroups (reversible Petri nets). I intend to prove …

May 24, 2006, 2:15 p.m.
Michał Strojnowski (Uniwersytet Warszawski)
Impossibility Proofs for Distributed Computing
Many problems have no solution in distributed computing. One of the best known examples is Byzantine Generals Problem, for which it is shown that if at least one third of the generals are malicious, there …

May 10, 2006, 2:15 p.m.
Slawomir Lasota (joint work with Wojciech Rytter) (Uniwersytet Warszawski)
On language and bisimulation equivalence of contextfree processes
In contrast to language equivalence, being undecidable for (normed) contextfree grammars, the bisimulation equivalence is decidable; and it is even polynomial for normed grammars.The fastest known algorithm for checking bisimulation equivalence worked in $O(n^{13})$ time. …