Seminars
29.03.2017 16:15 TBA 
Theoretical computer science TBA 
25.01.2017 16:15 01.03.2017 16:15 Grzegorz Guśpiel 
Theoretical computer science Partial Visibility Representation Extension Problem 
We study a class of graphs that have a special geometric representation. By a bar visibility representation of an undirected graph we mean a function that associates with each vertex of a graph a horizontal line segment in such a way, that between segments representing two ends of an edge there is a vertical strip (of visibility). In case of directed graphs, we additionally assume that the visibility is from the bottom to the top, that is the line segment representing the source of the edge is below the one for the target. Graphs admitting such representations are well understood and can be recognized in linear time, both in the undirected and in the directed case. We work in a more subtle setting, where line segments are already associated with some vertices of a graph, and the question is if this can be extended to a bar visibility representation of an entire graph. We prove some results on complexity of this kind of problems. This is joint work with Steven Chaplick, Grzegorz Gutowski, Tomasz Krawczyk and Giuseppe Liotta. The manuscript is available here: https://arxiv.org/abs/1512.00174 
Poprzednie referaty
25.01.2017 12:00 Sylwester Klocek 
Computer science foundations Incompleteness, Undecidability and Automated Proofs by Cristian S. Calude and Declan Thompson 
Incompleteness and undecidability have been used for many years as arguments against automatising the practice of mathematics. The advent of powerful computers and proofassistants – programs that assist the development of formal proofs by humanmachine collaboration – has revived the interest in formal proofs and diminished considerably the value of these arguments. In this paper we discuss some challenges proofassistants face in handling undecidable problems – the very results cited above – using for illustrations the generic proofassistant Isabelle. 
24.01.2017 Kamil Sałaś 
Cryptology Lower Bounds for Discrete Logarithms 
In the talk we will present the computational complexity of the discrete logarithm in the context of "generic algorithms", that is, algorithms which do not exploit any special properties of the encodings of group elements, other than the property that each group element is encoded as unique binary string. For discrete logarithm, any generic algorithm must perform Ω(p^1/2) group operations, where p is the largest prime dividing the order of the group. 
19.01.2017 Paweł Petecki Akademia GórniczoHutnicza 
Combinatorial Optimization Symmetry breaking polynomial 
Let G be a graph, and let Γ= Aut G. A coloring c of G is symmetrybreaking if for every nonidentity automorphism φ in Γ, there is some vertex v of G such that c(v)≠c(φ(v)). There has been a lot of work on the minimum number of colors in a symmetrybreaking coloring of G. We discuss here a different problem: counting the number of kcolorings that are symmetry breaking. The tool, as is frequently the case for problems such as this one, is Möbius inversion. To solve this problem we define symmetry breaking polynomial ψ_{G}. For positive integer k (number of colors), ψ_{G}(k) is the number of kcolorings that break all nontrivial symmetries of the graph G. 
18.01.2017 16:15 Marian Mrozek 
Theoretical computer science The discrete charm of Morse theory 
The lecture will start with recalling P.S. Alexandroff's Theorem (1937) on mutual equivalence of posets and T_{0} topologies on finite sets. Next, we will outline the combinatorial version of the classical Morse Theory presented by R. Forman in 1998. Then, we will elaborate Forman's ideas towards the combinatorial topological dynamics with potential applications in Big Data problems and time series. The topics of the lecture will be expanded in a course for PhD students in the summer semester 2016/17. 
18.01.2017 12:00 Michał Ziobro 
Computer science foundations Inhabitation in SimplyTyped LambdaCalculus through a LambdaCalculus for Proof Search by Jose Espırito Santo, Ralph Matthes, Luıs Pinto 
Kontynuacja seminarium z 23.11.2016 
17.01.2017 Grzegorz Bukowiec 
Cryptology A quasipolynomial algorithm for discrete logarithm in finite fields of small characteristic 
Until recently, all the algorithms for computing discrete logarithm had a subexponential complexity of type L(1/3), similar to the factorization problem. In this talk we'll discuss a heuristic algorithm that provides quasipolynomial complexity for discrete logarithm in finite fields of small characteristic and that even for other cases still surpasses the Function Field Sieve method. References: [1] R. Barbulescu, P. Gaudry, A. Joux, E. Thomé, A quasipolynomial algorithm for discrete logarithm in finite fields of small characteristic (pdf) 
11.01.2017 16:15 Patryk Mikos 
Theoretical computer science Online coloring of intervals with bandwidth 
We study the online interval coloring problem with bandwidth. The input is a sequence of pairs J_{i}= (I_{i},w_{i}) where I_{i} is an interval on the real line and w_{i} is a real number from (0,1]. In this setting a proper coloring is a function f:J_{i }→N such that for each color c and any point p on the real line, the sum of bandwidths of intervals containing p and colored by c does not exceed 1. The best known lower bound on the competitive ratio in this problem is 24/7. We present an explicit strategy for Presenter that increases the competitive ratio ifor this problem to at least 4.1626. 
11.01.2017 12:00 Patryk Mikos 
Computer science foundations ON THE NUMBER OF DISTINCT LANGUAGES ACCEPTED BY FINITE AUTOMATA WITH n STATES by Michael Domaratzki, Derek Kisman and Jeffrey Shallit 
We give asymptotic estimates and some explicit computations for both the number of distinct languages and the number of distinct finite languages over a kletter alphabet that are accepted by deterministic finite automata (resp. nondeterministic finite automata) with n states. 
10.01.2017 Szymon Policht 
Cryptology Faster operations on elliptic curves using Edwards curves 
Elliptic curve cryptography is a broad and commonly used section of modernday cryptography. Because of that, the speed of elliptic curve operations directly impacts the performance of many current systems. In this talk we'll show how to speed up those operations using Edwards curves. References: [1] Bernstein D.J., Lange T. (2007) Faster Addition and Doubling on Elliptic Curves. In: Kurosawa K. (eds) Advances in Cryptology – ASIACRYPT 2007. ASIACRYPT 2007. Lecture Notes in Computer Science, vol 4833. Springer, Berlin, Heidelberg (https://eprint.iacr.org/2007/286.pdf) 
05.01.2017 14:15 Jan Derbisz, Jakub Łabaj 
Algorytmika How to sort by walking on a tree 
We consider a tree with n vertices. On vertex number x there is a box with label p(x), with the function p being a permutation of {1,2,...,n}. A robot is walking on the tree, carrying at most one box at a time. If a box is placed where robot is standing, it can swap this box with the one being carried. The robot's goal is to sort the boxes, placing each one at the vertex with its number. The paper by D. Graf gives an algorithm computing the shortest possible robot's walk in quadratic time, as well as the proof that the problem becomes NPcomplete if planar graphs are considered instead of trees. 
04.01.2017 12:00 Konrad Kalita 
Computer science foundations ANALYTIC MODELS AND AMBIGUITY OF CONTEXTFREE LANGUAGES by Philippe Flajolet 
We establish that several classical contextfree languages are inherently ambiguous by proving that their counting generating functions, when considered as analytic functions, exhibit some characteristic form of transcendental behaviour. To that purpose, we survey some general results on elementary analytic properties and enumerative uses of algebraic functions in relation to formal languages In particular, the paper contains a general density theorem for unambiguous contextfree languages. 
03.01.2017 
Cryptology (Cancelled) 
22.12.2016 16:15 Łukasz Majcher, Jan Szczepaniec 
Combinatorial Optimization Convex ppartitions of bipartite graphs 
A set of vertices X of a graph G is convex if no shortest path between two vertices in X contains a vertex outside X. We prove that for fixed p ≥ 1, all partitions of the vertex set of a bipartite graph into p convex sets can be found in polynomial time. 
21.12.2016 16:15 Maciej Bendkowski 
Theoretical computer science Boltzmann samplers: a framework for random generation of combinatorial structures with an application to lambda calculus 
In their seminal paper, Duchon et al. proposed a surprisingly simple, generalpurpose framework of Boltzmann samplers meant for random generation of combinatorial structures. In this talk we revisit their method and discuss its elegant relation with analytic combinatorics as well as important practical implementation details. Finally, we discuss the application of Boltzmann samplers to the random generation of lambda terms used, e.g. in testing functional programming compilers. 
20.12.2016 12:00 Bartłomiej Puget 
Cryptology An introduction to quantum computing and cryptography II 
15.12.2016 14:15 Michał Glapa, Franciszek Stokowacki 
Algorytmika Maximum matching with algebraic methods 
In 2006, a celebrated result by Mucha and Sankowski stated that the maximum matching problem can be done by Gaussian elimination. The complexity of this algorithm depends on matrix multiplication, but certainly beats O(n^{2.5}) longstanding record of MicaliVazirani algorithm. 
15.12.2016 Anna Kobak 
Combinatorial Optimization Open problems in graph theory concerning minors. 
We mentioned following open problems in graph theory:

14.12.2016 16:15 Grzegorz Matecki 
Theoretical computer science TwoDimensional Irregular Packing Problem 
We present results on packing irregular shapes onto given sheets of material. 
14.12.2016 12:00 Piotr Wójcik 
Computer science foundations Enumeration and random generation of accessible automata by Frederique Bassino and Cyril Nicaud 
We present a bijection between the A_n of deterministic and accessible automata with n states on a kletters alphabet and some diagrams, which can themselves be represented as partitions of a set of kn + 1 elements into n nonempty subsets. This combinatorial construction shows that the asymptotic order of the cardinality of A_n is related to the Stirling number. Our bijective approach also yields an efficient random sampler, for the uniform distribution, of automata with n states, its complexity is O(n^3/2), using the framework of Boltzmann samplers. 
13.12.2016 12:00 Krzysztof Kleiner 
Cryptology An introduction to quantum computing and cryptography I 
In this talk we're going to discuss quantum informatics and its impact on the field of cryptography. We will introduce the basic concepts of quantum computing as well as cryptography based on Quantum Key Distribution scheme, one of the aspects of quantum informatics which already is being used in practice. Then we will present Shor's algorithm for polynomialtime factorization, responsible for the cryptosystems based on the hardness of factorization or discrete logarithm (in abelian groups) being no longer secure against an adversary with access to a quantum computer.

08.12.2016 Lech Duraj 
Algorytmika A short tale of matrix multiplication 
In recent years, some new algorithms for matrix multiplication problem were presented. Each of them is, however, only slightly faster than previous ones, while requiring substantially more complex analysis. Because of this, the longstanding question of optimal matrix multiplication algorithm seems even harder. In my presentation, a short survery of the matrix multiplication algorithm is given. The presentation is based on François Le Gall's survey lecture of 2014. 
08.12.2016 Zygmunt Łenyk 
Combinatorial Optimization Rendezvous on the line. 
This is one of a handful of rendezvous problems where two players must find one another in a certain structured domain. In line case, players are placed on the line with distance 2, without knowing neither on which side is their partner, nor the direction of the line. I'll concentrate on the symmetric case where players must follow a specific (but maybe mixed) strategy. The conjecture is that best expected time of meeting two players equals 4.25. 
07.12.2016 12:00 Jakub Brzeski 
Computer science foundations ENUMERATION OF FORMAL LANGUAGES by Michael Domaratzki 
We survey recent results on the enumeration of formal languages. In particular, we consider enumeration of regular languages accepted by deterministic and nondeterministic finite automata with n states, regular languages generated by regular expressions of a fixed length, and !regular languages accepted by Müller automata. We also survey the uncomputability of enumeration of contextfree languages and more general structures. 
06.12.2016 Marek Rusinowski 
Cryptology Security of instant messaging applications. 
Nowadays billions of people around the world are sharing sensitive information using instant messaging applications. We will look into the current state of IM security, the problems in this area and a few encryption protocolsOTR and Signal Protocol in particularthat provide security features desired by users. 
01.12.2016 Aleksandra Mędrek, Krzysztof Maziarz 
Algorytmika Navigating Central Path with Electrical Flows: from Flows to Matchings, and Back 
The paper by Aleksander Mądry describes a new approach to the maximum flow problem. We define an electrical flow by assigning resistances to every edge and minimizing total energy instead of maximizing flow. Any flow network can be reduced to some electrical flow problem, using auxiliary reductions to some bipartite matching problems. The main result is a new maximum flow algorithm, working in O(m10/7). The presentation will cover a simpler, O(m3/2) version of the algorithm. 
01.12.2016 Patryk Urbański 
Combinatorial Optimization Coloring Ordinary Maps, Maps of Empires and Maps of the Moon 
A short review of generalized map coloring problems:

01.12.2016 Mateusz Twaróg 
Combinatorial Optimization Second Neighborhood via First Neighborhood in Digraphs 
30.11.2016 18:15 Bartosz Walczak 
Theoretical computer science Coloring curves that cross a fixed curve 
A class of graphs is χbounded if the chromatic number of all graphs in the class is bounded by some function of their clique number. String graphs are intersection graphs of curves in the plane. Significant research in combinatorial geometry has been devoted to understanding the classes of string graphs that are χbounded. In particular, it is known since 2012 that the class of all string graphs is not χbounded. We prove that for every integer t≥1, the class of intersection graphs of curves in the plane each of which crosses a fixed curve in at least one and at most t points is χbounded. This result is best possible in several aspects; for example, the upper bound t on the number of crossings with the fixed curve cannot be dropped. As a corollary, we obtain new upper bounds on the number of edges in socalled kquasiplanar topological graphs. This is joint work with Alexandre Rok. 
30.11.2016 12:00 Yauheni Ananchuk 
Computer science foundations ALGEBRAIC FOUNDATIONS FOR QUALITATIVE CALCULI AND NETWORKS by ROBIN HIRSCH, MARCEL JACKSON, AND TOMASZ KOWALSKI 
Binary Constraint Problems have traditionally been considered as Network Satisfaction Problems over some relation algebra. A constraint network is satisfable if its nodes can be mapped into some representation of the relation algebra in such a way that the constraints are preserved. A qualitative representation is like an ordinary representation, but instead of requiring (a ; b) = a j b , as we do for ordinary representations, we only require that. A constraint network is qualitatively satisfable if its nodes can be mapped to elements of a qualitative representation, preserving the constraints. If a constraint network is satisfable then it is clearly qualitatively satisfable, but the converse can fail. However, for a wide range of relation algebras including the point algebra, the Allen Interval Algebra, RCC8 and many others, a network is satisfable if and only if it is qualitatively satisfable. Unlike ordinary composition, the weak composition arising from qualitative representations need not be associative, so we can generalise by considering network satisfaction problems over nonassociative algebras. We prove that computationally, qualitative representations have many advantages over ordinary representations: whereas many finite relation algebras have only infnite representations, every finite qualitatively representable algebra has a finite qualitative representation; the representability problem for (the atom structures of) finite nonassociative algebras is NPcomplete; the network satisfaction problem over a finite qualitatively representable algebra is always ; the validity of equations over qualitative representations is coNPcomplete. On the other hand we prove that there is no finite axiomatisation of the class of qualitatively representable algebra 
29.11.2016 Anna Kobak 
Cryptology Breaking RSA vs Factoring in generic ring model 
In the talk we present results of Aggarwal and Maurer [1], who showed that a generic ring algorithm for breaking RSA with modulus $N$ can be converted into an algorithm for factoring $N$. The results imply that any attempt at breaking RSA without factoring $N$ will be nongeneric and hence will have to manipulate the particular bitrepresentation of the input modulo $N$. This provides new evidence that breaking RSA may be equivalent to factoring the modulus.
References: [1] D. Aggarwal, U. Maurer, Breaking RSA Generically is Equivalent to Factoring, EUROCRYPT 2009 
24.11.2016 Wojciech Łopata 
Combinatorial Optimization Several open problems from game theory, graph theory and combinatorics. 
I'll briefly introduce the audience to two unrelated areas: book embedding and mechanism design, and walk through some open problems in those areas. 
24.11.2016 Dominika Salawa, Jakub Cisło 
Algorytmika Greedy algorithms for Steiner forest 
The paper, resolves a longstanding open question: is the greedy approach for Steiner forest problem optimal up to multiplicative constant? The result by Anupam Gupta and Amit Kumar proves that in fact it is, with constant being at most 96. While some approximation algorithms for this problem, using linear programming, were previously known, this is the first known bound for a greedy algorithm. 
23.11.2016 Piotr Danilewski 
Theoretical computer science Functional Code Building 

23.11.2016 Michał Ziobro 
Computer science foundations Inhabitation in SimplyTyped LambdaCalculus through a LambdaCalculus for Proof Search by Jos´e Espırito Santo, Ralph Matthes, Luıs Pinto 
A new, comprehensive approach to inhabitation problems in simplytyped lambdacalculus is shown, dealing with both decision and counting problems. This approach works by exploiting a representation of the search space generated by a given inhabitation problem, which is in terms of a lambdacalculus for proof search that the authors developed recently. The representation may be seen as extending the CurryHoward representation of proofs by lambdaterms, staying within the methods of lambdacalculus and type systems. Our methodology reveals inductive descriptions of the decision problems, driven by the syntax of the proofsearch expressions, and the end products are simple, recursive decision procedures and counting functions. 
22.11.2016 Aleksandra Nowak 
Cryptology Lattice Cryptography and The Learning With Errors Problem 
17.11.2016 Paweł Kubiak 
Combinatorial Optimization Succinct Data Structures 
17.11.2016 Patryk Gołębiowski, Wojciech Kruk 
Algorytmika Lower Bounds in the Preprocessing and Query Phases of Routing Algorithms 
In the last decade, there has been a substantial amount of research in finding routing algorithms designed specifically to run on realworld graphs. The paper by Colin White analyzes some of these algorithms and gives lower bounds for their complexity. 
16.11.2016 Bartłomiej Bosek 
Theoretical computer science Every digraph is majority 4choosable 
A majority coloring of a digraph is a coloring of its vertices such that for each vertex at most half of its outneighbors has the same color as that vertex. A digraph D is majority kchoosable if for any assignment of color lists of size k to the vertices there is a majority coloring of D from these lists. We prove the statement in the title. This gives a positive answer to a question posed recently in 1. This is a joint work with Marcin Anholcer and Jarosław Grytczuk. 
16.11.2016 Michał Zieliński 
Computer science foundations Most programs stop quickly or never halt by Cristian S. Calude and Michael A. Stay 
The aim of this paper is to provide a probabilistic, but nonquantum, analysis of the Halting Problem. Our approach is to have the probability space extend over both space and time and to consider the probability that a random Nbit program has halted by a random time.We postulate an a priori computable probability distribution on all possible runtimes and we prove that given an integer k >0, we can effectively compute a time bound T such that the probability that an Nbit program will eventually halt given that it has not halted by T is smaller than 2^{−k}. We also show that the set of halting programs (which is computably enumerable, but not computable) can be written as a disjoint union of a computable set and a set of effectively vanishing probability. Finally, we show that “long” runtimes are effectively rare. More formally, the set of times at which an Nbit program can stop after the time 2^{N+constant} has effectively zero density. 
15.11.2016 Piotr Kawałek 
Cryptology Teoretyczne podstawy kryptoanalizy 
Celem referatu jest przedstawienie teoretycznych modeli ataków kryptoanalitycznych oraz tematów pokrewnych wraz z przykładami. 
10.11.2016 Magdalena Gargas, Mateusz Jachna 
Algorytmika Max flows in O(nm) time, or better 
A new maxflow algorithm with O(nm + m16/15 log2 n) time complexity is presented. By combining this with previous results, an O(nm) algorithm may be obtained, resolving a longstanding open question. This work is due to James B. Orlin. 
10.11.2016 Grzegorz Bukowiec 
Combinatorial Optimization On more variants of the Majority Problem 
09.11.2016 26.10.2016 Adam Polak 
Theoretical computer science Open problems in online and approximation algorithms 
During the talk I will present several promising open problems including:

09.11.2016 Wojciech Kruk 
Computer science foundations On the generic undecidability of the Halting Problem for normalized Turing machines by Alexander Rybalov 
Hamkins and Miasnikov presented in 2004 a generic algorithm deciding the classical Halting Problem for Turing machines with oneway tape on a set of asymptotic probability one (on a socalled generic set). Rybalov in 2007 showed that there is no generic algorithm deciding this problem on strongly generic sets of inputs (some subclass of generic sets). In this paper we prove that there is no generic algorithm deciding the Halting Problem for normalized Turing machines on generic sets of inputs. Normalized Turing machines have programs with the following natural restriction: internal states with large indices are not allowed at the beginning of the program. This condition does not reduce the class of computable functions because for every Turing machine there exists a normalized Turing machine which computes the same function. Our proof holds for machines with oneway and twoway tape. It also implies that the HamkinsMiasnikov algorithm is not generic for normalized Turing machines. 
08.11.2016 Patryk Gołębiowski 
Cryptology Advanced Encryption Standard 
Advanced Encryption Standard (AES) is one of the most popular and widely adopted symmetric encryption scheme. In the talk we discuss how it works and why it is considered safe by the U.S. National Institute of Standards and Technology to use it for protecting classified information. 
03.11.2016 Gabriel Jakóbczak 
Combinatorial Optimization Proper orientations of some types of graphs 
Let G be a simple graph. We say that orientation of graph G is proper if for every pair of adjacent veritces u and v their indegrees are different. It was proved by Mieczysław Borowiecki, Jarosław Grytczuk and Monika Pilśniak that for every simple graph exists its proper orientation. Now we can define the proper orientation number of graph G as the minimum of the maximum indegree, taken over all proper orientations of G. We show that for some classes of bipartite graphs their proper orientation number is less than or equal to 6. We also show that this parameter is at most 4 for graphs which are trees and proof of that fact leads to a polynomialtime algorithm of finding proper orientation of such graphs.
Fiachra Knox, Sebastián González Hermosillo de la Maza, Bojan Mohar, and Cláudia Linhares Sales. Proper Orientations of Planar Bipartite Graphs. pages 26, sep 2016. 
03.11.2016 Krzysztof Francuz, Szymon Łukasz 
Algorytmika Fast and simple connectivity in graph timelines 
The presented paper (by J. Łącki and A. Karczmarz) deals with graph timelines  graphs with edges being created and destroyed over time. There is an effective algorithm for answering queries about reachability (finding a path between two given vertices) and biconnectivity (two disjoint paths) over some given time intervals. 
27.10.2016 Dawid Pyczek, Jakub Rówiński 
Algorytmika Faster deterministic sorting and priority queues in linear space 
The O(n log n) lower bound for sorting is valid only if the sorted objects allow no operations except comparing. For sorting integers, the bound can be broken  Mikkel Thorup's result of 1997 shows an O (n (log log n)^{2}) algorithm for sorting arbitrary integers. 
27.10.2016 Magdalena Gargas 
Combinatorial Optimization The geometry of nesting problems: A tutorial 
26.10.2016 Wojciech Łopata 
Computer science foundations Universality and Almost Decidability by Cristian S. Calude and Damien Desfontaines 
We present and study new definitions of universal and programmable universal unary functions and consider a new simplicity criterion: almost decidability of the halting set. A set of positive integers S is almost decidable if there exists a decidable and generic (i.e. a set of natural density one) set whose intersection with S is decidable. Every decidable set is almost decidable, but the converse implication is false. We prove the existence of infinitely many universal functions whose halting sets are generic (negligible, i.e. have density zero) and (not) almost decidable. One result—namely, the existence of infinitely many universal functions whose halting sets are generic (negligible) and not almost decidable—solves an open problem in [9]. We conclude with some open problems. 
25.10.2016 Marcin Briański 
Cryptology Unifying Zeroknowledge Proofs of Knowledge 
We present a simple zeroknowledge proof of knowledge protocol of which many protocols in the literature are instantiations. These include Schnorr's protocol for proving knowledge of a discrete logarithm, the FiatShamir and GuillouQuisquater protocols for proving knowledge of a modular root, protocols for proving knowledge of representations (like Okamoto's protocol), protocols for proving equality of secret values, a protocol for proving the correctness of a DiffieHellman key, protocols for proving the multiplicative relation of three commitments (as required in secure multiparty computation), and protocols used in credential systems. This shows that a single simple treatment (and proof), at a high level of abstraction, can replace the individual previous treatments. Moreover, one can devise new instantiations of the protocol. [1] Ueli Maurer, Unifying Zeroknowledge Proofs of Knowledge, Progress in Cryptology – AFRICACRYPT 2009, Vol. 5580 LNCS, pp 272286

20.10.2016 Helena Borak 
Combinatorial Optimization Exact algorithms for the twodimensional strip packing problem with and without rotations 
We propose exact algorithms for the twodimensional strip packing problem (2SP) with and without 90 degree rotations. We first focus on the perfect packing problem (PP), which is a special case of 2SP, wherein all given rectangles are required to be packed without wasted space, and design branchandbound algorithms introducing several branching rules and bounding operations. A combination of these rules yields an algorithm that is especially efficient for feasible instances of PP. We then propose several methods of applying the PP algorithms to 2SP. Our algorithms succeed in efficiently solving benchmark instances of PP with up to 500 rectangles and those of 2SP with up to 200 rectangles. They are often faster than existing exact algorithms specially tailored for problems without rotations. 
20.10.2016 Mateusz Twaróg, Patryk Urbański 
Algorytmika Disjoint Set Union with randomized linking 
The most popular version of FindUnion algorithm uses path compression and linking by rank. The presented work of Goel, Khanna, Larkin and Tarjan gives an analysis of the same algorithm, but with arbitrary (randomized) linking. 
19.10.2016 Bartosz Walczak 
Theoretical computer science Common tangents of two disjoint polygons in linear time and constant workspace 
A tangent of a polygon is a line touching but not crossing the polygon. Two disjoint polygons can have four, two, or no common tangents, depending on whether the convex hulls of the polygons are disjoint, overlapping, or nested. We describe a very simple lineartime constantworkspace algorithm to compute all common tangents of two disjoint polygons, each given by a readonly array of its corners in a cyclic order. This is joint work with Mikkel Abrahamsen. 
19.10.2016 Pola Kyzioł 
Computer science foundations The domino problem for selfsimilar structures by Sebastian Barbieri and Mathieu Sablik 
We defne the domino problem for tilings over selfsimilar structures of $Z^d$ given by forbidden patterns. In this setting we exhibit nontrivial families of subsets with decidable and undecidable domino problem. 
18.10.2016 Grzegorz Jurdzinski 
Cryptology Timing attacks 
Cryptosystems like AES or RSA use algorithms which runtime depends on input data or using CPU cache. Basing on this fact an attacker can find secret keys by choosing inputs and carefully measuring time needed for computations. In this talk I will present such attacks and how to prevent them.

13.10.2016 Krzysztof Barański 
Combinatorial Optimization LevelOriented TwoDimensional Packing Algorithms 
13.10.2016 G. Bukowiec, S.Klocek 
Algorytmika FKT algorithm 
Counting all matchings in a given graph is a #Pcomplete problem. However, for planar graphs it can be done in polynomial time. The FKT algorithm does it by exploiting the connection between the notions of matrix determinant and matrix permanent. 
12.10.2016 Adam Polak 
Theoretical computer science Why is it hard to beat O(n^2) for Longest Common Weakly Increasing Subsequecnce? 
11.10.2016 Michał Zieliński 
Cryptology SafeDeflate: compression without leaking secrets 
CRIME and BREACH attacks on TLS/SSL leverage the fact that compression ratio is not hidden by encryption to recover content of secrets. We introduce SafeDeflate—a modification of a standard Deflate algorithm which compression ratio does not leak information about secret tokens. The modification is compatible with existing Deflate and gzip decompressors. We introduce a model in which attacker can obtain ciphertexts of arbitrary compressed plaintext containing secret values. Then we prove that SafeDeflate is secure in this model. 
06.10.2016 Bartłomiej Bosek 
Combinatorial Optimization A new variant of the game of cops and robber 
The talk presents a joint work of Jarosław Grytczuk, Joanna Sokół, Małgorzata ŚleszyńskaNowak. We consider the following metric version of the Cops and Robbers game. Let G be a simple graph and let k≥1 be a fixed integer. In the first round, Cop picks a subset of k vertices B={v_{1},v_{2},…,v_{k}} and then Robber picks a vertex u but keeps it in a secret. Then Cop asks Robber for a vector D_{u}(B)=(d_{1},d_{2},…,d_{k}) whose components d_{i}=d_{G}(u,v_{i}), i=1,2,…,k, are the distances from u to the vertices of B. In the second round, Robber may stay at the vertex u or move to any neighbouring vertex which is kept in a secret. Then Cop picks another k vertices and asks as before for the corresponding distances to the vertex occupied by Robber. And so on in every next round. The game stops when Cop determines exactly the current position of Robber. In that case, she is the winner. Otherwise, Robber is the winner (that is if Cop is not able to localize him in any finite number of rounds). Let ζ(G) denote the least integer k for which Cop has a winning strategy. Notice that this parameter is well defined since the inequality ζ(G)≤V(G) holds obviously. 
05.10.2016 Tomasz Kisielewski 
Computer science foundations Programy które są w stanie przeprowadzać rozumowania o swoich własnościach Proving properties of programs within their language 
Przedstawię wstępną wersję swojego programu badawczego, mającego ====== I will present an initial version of my research program, whosemain goal is to enable proving properties about programs within 
15.06.2016 Piotr Kawałek i Teodor Jerzak 
Computer science foundations Generalised and Quotient Models for Random And/Or Trees and Application to Satisfiability by Antoine Genitrini and Cécile Mailler: 
This article is motivated by the following satisfiability question: pick uniformly at random an and/or Boolean expression of length n, built on a set of k_n Boolean variables. What is the probability that this expression is satisfiable? asymptotically when n tends to infinity? The model of random Boolean expressions developed in the present paper is the model of Boolean Catalan trees, already extensively studied in the literature for a constant sequence. The fundamental breakthrough of this paper is to generalise the previous results for any (reasonable) sequence of integers which enables us, in particular, to solve the above satisfiability question. We also analyse the effect of introducing a natural equivalence relation on the set of Boolean expressions. This new quotient model happens to exhibit a very interesting threshold (or saturation) phenomena.

09.06.2016 Gwenaël Joret Université Libre de Bruxelles 
Algorithmic aspects of combinatorics Improved Approximation Algorithms for Hitting 3Vertex Paths 
We study the problem of deleting a minimum cost set of vertices from a 
08.06.2016 Kamil Pietruszka 
Computer science foundations Regular Combinators for String Transformations by Rajeev Alur Adam Freilich Mukund Raghothaman 
We focus on (partial) functions that map input strings to a monoid such as the set of integers with addition and the set of output strings with concatenation. The notion of regularity for such functions has been defined using twoway finitestate transducers, (oneway) cost register automata, and MSOdefinable graph transformations. In this paper, we give an algebraic and machineindependent characterization of this class analogous to the definition of regular languages by regular expressions. When the monoid is commutative, we prove that every regular function can be constructed from constant functions using the combinators of choice, split sum, and iterated sum, that are analogs of union, concatenation, and Kleene *, respectively, but enforce unique (or unambiguous) parsing. Our main result is for the general case of noncommutative monoids, which is of particular interest for capturing regular stringtostring transformations for document processing. We prove that the following additional combinators suffice for constructing all regular functions: (1) the leftadditive versions of split sum and iterated sum, which allow transformations such as string reversal; (2) sum of functions, which allows transformations such as copying of strings; and (3) function composition, or alternatively, a new concept of chained sum, which allows output values from adjacent blocks to mix. 
02.06.2016 http://wms.mat.agh.edu.pl/~knmd/index.php/ikonferencjanaukowaknmd/harmonogram/ 
Algorithmic aspects of combinatorics Konferencja Studencka na AGH 
01.06.2016 Szymon Borak 
Theoretical computer science Polynomial time algorithm for finding Hamiltonian cycles in thin grid graphs 
In general, Hamiltonian Cycle Problem is NPcomplete in triangular and square grids. In "Not being(super)thin or solid is hard: A study of grid Hamiltonicity" Arkin et al. claimed HCP for thin triangular grids and thin square grids to be NPcomplete as well. However the arguments they gave are incorrect. In fact we show that thin triangular grids as well as thin square grids always have HC. Moreover we show a linear algorithm for finding a HC in such graphs. 
01.06.2016 Piotr Bejda 
Computer science foundations PATTERN AVOIDANCE IS NOT P RECURSIVE by SCOTT GARRABRANT AND IGOR PAK 
Let F \subset S_k be a finite set of permutations and let C_n (F) denote the number of permutations avoiding the set of patterns F.

25.05.2016 Kolja Knauer Université AixMarseille 
Theoretical computer science Orienting triangulations  towards Schynyder woods on orientable surfaces 
We show that the edges of any triangulation of a closed surface different from the projective plane and the sphere can be oriented such that every vertex has nonzero outdegree divisble by three. This confirms a conjecture of Barát and Thomassen. We will explain why this is a first step towards the generalization of Schynyder woods from the plane to orientable surfaces and what is know 
19.05.2016 Miloš Stojaković University of Novi Sad 
Algorithmic aspects of combinatorics MakerBreaker games on random graphs 
Of all types of positional games, MakerBreaker games are probably the 
18.05.2016 Pola Kyzioł 
Computer science foundations NPCompleteness of a Combinator Optimization Problem by M. S. Joy and V. J. RaywardSmith 
We consider a deterministic rewrite system for combinatory logic over combinators $S,K,I,B,C,S',B'$, and $C'$. 
12.05.2016 Barłomiej Bosek 
Algorithmic aspects of combinatorics Coloring shiftchain hypergraphs 
05.05.2016 Jarosław Grytczuk 
Algorithmic aspects of combinatorics On some graph coloring problems 
28.04.2016 Wojciech Samotij Tel Aviv University 
Algorithmic aspects of combinatorics How does a typical finite metric space look like? 
27.04.2016 Michał Zieliński 
Computer science foundations Beta Reduction is Invariant, Indeed by Beniamino Accattoli and Ugo Dal Lago 
Slot and van Emde Boas weak invariance thesis states that reasonable machines can simulate each other within a polynomially overhead in time.Is lambda calculus a reasonable machine? Is there a way to measure the computational complexity of a lambda term? This paper presents the first complete positive answer to this longstanding problem. Moreover, our answer is completely machineindependent and based over a standard notion in the theory of lambda calculus: the length of a leftmostoutermost derivation to normal form is an invariant cost model. Such a theorem cannot be proved by directly relating lambda calculus with Turing machines or random access machines, because of the size explosion problem: there are terms that in a linear number of steps produce an exponentially long output. The first step towards the solution is to shift to a notion of evaluation for which the length and the size of the output are linearly related. This is done by adopting the linear substitution calculus (LSC), a calculus of explicit substitutions modelled after linear logic proof nets and admitting a decomposition of leftmostoutermost 
21.04.2016 Jarosław Grytczuk 
Algorithmic aspects of combinatorics On some problems in combinatorial number theory 
20.04.2016 Adam Polak 
Theoretical computer science On subposets of dimension two 
We study the maximum guaranteed size of a dimension two subposet of an nelement poset. A trivial lower bound of the order of n^{1/2} follows from the Dilworth's theorem. We show an upper bound of the order of n^{2/3} improving the n^{0.8295} result by Reiniger and Yeager. We also discuss promising methods for achieving a better lower bound. 
20.04.2016 Wojciech Kruk 
Computer science foundations On the equivalence of different presentations of Turner's bracket abstraction algorithm by Lukasz Czajka 
Turner's bracket abstraction algorithm is perhaps the most wellknown improvement on simple bracket abstraction algorithms. It is also one of the most studied bracket abstraction algorithms. The definition of the algorithm in Turner's original paper is slightly ambiguous 
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