Organizers

prof. dr hab. Mikołaj Bojańczyk
prof. dr hab. Damian Niwiński

Information

Wednesdays, 2:15 p.m. , room: 5440

Research fields

List of talks

April 20, 2011, 2:15 p.m.
Laurent Braud (Uniwersytet Warszawski)
Limits of interpretations and unfoldings
The original motivation was the characterisation of more structureswith decidable MSO theory. We consider the transformation approach :operations that preserve decidability include MSO-interpretations andunfoldings, which can be used to build the Caucal hierarchy. In anattempt …
April 13, 2011, 2:15 p.m.
Paweł Parys (Uniwersytet Warszawski)
The excluded grid theorem
I will present a proof of the excluded grid theorem of Robertson and Seymour: a graph has no large grid minor if and only if it has small tree-width.
April 6, 2011, 2:15 p.m.
Michał Pilipczuk (Uniwersytet Warszawski)
Solving problems parameterized by tree-width in single exponential time: a logical approach
We introduce a variant of modal logic on graphs, dubbed EXISTENTIAL COUNTINGMODAL LOGIC (ECML), which captures a vast majority of problems knownto be tractable in single exponential time when parameterized by treewidth. Itappears that all …
March 30, 2011, 2:15 p.m.
Wojciech Czerwiński (Uniwersytet Warszawski)
Towards decidability of weak bisimilarity on BPP
Consider transition system generated by commutative context-free grammar,so called BPP. Strong bisimilarity is known to be PSPACE-complete on this classof infinite graphs, weak bisimilarity (with possible epsilon transitions) is important and longstanding open problem.I will …
March 23, 2011, 2:15 p.m.
Mikołaj Bojańczyk (Uniwersytet Warszawski)
No satisfiability measure for first-order logic on graphs
Consider MSO on graphs, with quantification over sets of edges andsets of nodes.Tree-width is a good measure of graphs for this logic because: a) for every k,satisﬁability is decidable over graphs of tree-width at most …
March 16, 2011, 2:15 p.m.
Marcin Bilkowski (Uniwersytet Warszawski)
Complements of unambiguous languages.
An automaton is unambiguous if it has at most one accepting run for every input.A language is unambiguous if there exists an unambiguous automaton recognizingthat language. It is known that not all regular languages of …
March 9, 2011, 2:15 p.m.
Sławomir Lasota (Uniwersytet Warszawski)
Automata with group actions
Our motivating question is a Myhill-Nerode theorem for infinitealphabets. We consider several kinds of those: alphabets whose letterscan be compared only for equality, but also ones with more structure,such as a total order or a …
March 2, 2011, 2:15 p.m.
Vince Barany (Uniwersytet Warszawski)
joint work with Balder ten Cate and Luc Segoufin (Guarded negation)
We consider restrictions of first-order logic and least fixpoint logic in which all occurrences of negation are required to be guarded by an atomic predicate. The so obtained guarded negation fragments GNFO and GNFP naturally …
Feb. 23, 2011, 2:15 p.m.
Alessandro Facchini (Uniwersytet Warszawski)
joint work with Balder ten Cate (Characterizations of EF over Infinite Trees)
We provide several equivalent effective characterizations of EF (the modallogic of the descendant relation) on arbitrary trees. Morespecifically, we prove that, for EF-bisimulation invariantproperties of trees, being definable by an EF formula, being aBorel set, …
Feb. 2, 2011, 2:15 p.m.
Henryk Michalewski (Uniwersytet Warszawski)
joint result with D. Niwinski). (On the separation property of regular languages)
We will show that separation property fails for the regular languagesof index (1,3) on infinite trees. More specifically, we willconstruct two disjoint tree languages B_1 and B_2 of index (1,3) notseparable by any set C …
Jan. 26, 2011, 2:15 p.m.
Crocodile Dundee (Tasmania)
Holiday
Because of 26.01 which is Australia Day we have holiday. You should use those days to prepare for next week seminar :).
Jan. 19, 2011, 2:15 p.m.
Diego Figueira (Uniwersytet Warszawski)
joint work with S. Figueira, S. Schmitz and Ph. Schnoebelen (Ackermannian and Primitive-Recursive Bounds with Dickson’s Lemma)
Dickson’s Lemma is a simple yet powerful tool widely used indecidability proofs, especially when dealing with counters or relateddata structures in algorithmics, verification and model-checking,constraint solving, logic, etc. While Dickson’s Lemma is well-known,most computer scientists …
Jan. 12, 2011, 2:15 p.m.
Wojciech Czerwiński (Uniwersytet Warszawski)
Fast equivalence checking for normed context-free processes. Joint work with Sławomir Lasota.
We consider graphs generated by context free grammars and ask the question if given two states in such an infinite graph are equivalent. I will talk about the new algorithm which answers this question using …
Jan. 5, 2011, 2:15 p.m.
Mikołaj Bojańczyk (Uniwersytet Warszawski)
Ramsey Theorems for Compact Colors. Joint work with Eryk Kopczyński and Szymon Toruńczyk
When applied to omega-words, the Ramsey Theorem says the following. Suppose that finite factors (=infixes) of an omega-word are colored by a finite number of colors. Then one factorize a suffix of the omega-word so …
Dec. 8, 2010, 2:15 p.m.
Mikołaj Bojańczyk (Uniwersytet Warszawski)
Efficient evaluation for temporal logic on changing XML documents joint work with Diego Figueira
We consider a sequence $t_1,\ldots,t_k$ of XML documents that isproduced by a sequence of local edit operations. To describeproperties of such a sequence, we use a temporal logic. The logic cannavigate both in time and …