Seminaria
25.11.2020 12:14 Wojtek Grabis 
Podstawy Informatyki (Optimal) Duplication is not Elementary Recursive by Andrea Asperti, Paolo Coppola and Simone Martini 
In 1998 Asperti and Mairson proved that the cost of reducing a lambdaterm using an optimal lambdareducer (a la L´evy) cannot be bound by any elementary function in the number of sharedbeta steps. We prove in this paper that an analogous result holds for Lamping’s abstract algorithm. That is, there is no elementary function in the number of shared beta steps bounding the number of duplication steps of the optimal reducer. This theorem vindicates the oracle of Lamping’s algorithm as the culprit for the negative result of Asperti and Mairson. The result is obtained using as a technical tool Elementary Affine Logic. 
26.11.2020 14:15 Jan Mełech, Michał Zwonek 
Algorytmika On the FineGrained Complexity of Parity Problems 
26.11.2020 16:15 Marcin Serwin 
Optymalizacja Kombinatoryczna (m,n)cycle cover conjectures 
An (m,n)cycle cover is a covering of a graph consisting of m cycles such that every edge is covered exactly n times. For positive integers m, n it is natural to ask what family of graphs have (m,n)cycle covers. The answers are known for some values, but for many others, they are conjectured or totally open. (the seminar will only be online) 
26.11.2020 17:00 Krzysztof Potępa 
Optymalizacja Kombinatoryczna Erdős–Hajnal conjecture 
A wellknown theorem of Erdős states that there exists a graph on n vertices, with no clique or independent set of a size larger than O(log n). The Erdős–Hajnal conjecture says it is very different if we consider families of graphs defined by forbidden induced subgraphs. Specifically, it is conjectured that for every graph H, there exists a constant δ(H) such that every Hfree graph G has either a clique or independent set of size V(G)^{δ(H)}. We will discuss some classes of graphs for which the conjecture has been proven, as well as weaker theorems that hold for all graphs. (the seminar will only be online) 
02.12.2020 12:14 Wojciech Węgrzynek 
Podstawy Informatyki The repetition threshold for binary rich words by James Currie, Lucas Mol and Narad Rampersad 
A word of length n is rich if it contains n nonempty palindromic factors. An infinite word is rich if all of its finite factors are rich. Baranwal and Shallit produced an infinite binary rich word with critical exponent $2 + \Sqrt{2}/2$ ( = 2.707) and conjectured that this was the least possible critical exponent for infinite binary rich words (i.e., that the repetition threshold for binary rich words is $2 + \Sqrt{2}/2$ ). In this article, we give a structure theorem for infinite binary rich words that avoid 14/5powers (i.e., repetitions with exponent at least 2.8). As a consequence, we deduce that the repetition threshold for binary rich words is $2 + \Sqrt{2}/2$ , as conjectured by Baranwal and Shallit. This resolves an open problem of Vesti for the binary alphabet; the problem remains open for larger alphabets.

03.12.2020 14:15 Rafał Kilar, Szymon Salabura 
Algorytmika Tetris is NPhard even with O(1) rows or columns 
09.12.2020 12:14 Katarzyna Król 
Podstawy Informatyki A Lower Bound of the Number of Rewrite Rules Obtained by Homological Methods by Mirai Ikebuchi 
It is wellknown that some equational theories such as groups or boolean algebras can be defined by fewer equational axioms than the original axioms. However, it is not easy to determine if a given set of axioms is the smallest or not. Malbos and Mimram investigated a general method to find a lower bound of the cardinality of the set of equational axioms (or rewrite rules) that is equivalent to a given equational theory (or term rewriting systems), using homological algebra. Their method is an analog of Squier’s homology theory on string rewriting systems. In this paper, we develop the homology theory for term rewriting systems more and provide a better lower bound under a stronger notion of equivalence than their equivalence. The author also implemented a program to compute the lower bounds. 
16.12.2020 12:15 Weronika Loreńczyk 
Podstawy Informatyki The Fractal Dimension of SAT Formulas by Carlos Ansotegui, Maria Bonet , Jesus GiraldezCru and Jordi Levy 
Modern SAT solvers have experienced a remarkable progress on solving industrial instances. Most of the techniques have been developed after an intensive experimental process. It is believed that these techniques exploit the underlying structure of industrial instances. However, there is not a precise definition of the notion of structure. Recently, there have been some attempts to analyze this structure in terms of complex networks, with the longterm aim of explaining the success of SAT solving techniques, and possibly improving them. We study the fractal dimension of SAT instances with the aim of complementing the model that describes the structure of industrial instances. We show that many industrial families of formulas are selfsimilar, with a small fractal dimension. We also show how this dimension is affected by the addition of learnt clauses during the execution of SAT solvers. 
01.01.2021 16:15 Grzegorz Gutowski 
Informatyka Teoretyczna TBA  Gutowski 
01.01.2021 16:15 Bartosz Walczak 
Informatyka Teoretyczna TBA  Walczak 
01.01.2021 16:15 Paweł Idziak 
Informatyka Teoretyczna Modular circuits satisfiability of intermediate complexity 
In our paper [LICS'18] a generalization of Boolean circuits to arbitrary finite algebras was introduced and applied to sketch P versus NPcomplete borderline for circuits satisfiability over algebras from congruence modular varieties. However nilpotent but not supernilpotent algebras have not been put on any side of this borderline. This paper provides a broad class of examples, lying in this grey area, and show that, under the Exponential Time Hypothesis and Strong Exponential Size Hypothesis (saying that Boolean circuits need exponentially many modular counting gates to produce Boolean conjunctions of any arity), satisfiability over these algebras have intermediate complexity. We also sketch how these examples could be used as paradigms to fill the nilpotent versus supernilpotent gap in general. Our examples are striking in view of the natural strong connections between circuits satisfiability and Constraint Satisfaction Problem for which the dichotomy was shown by Bulatov and Zhuk. Joint work with Piotr Kawałek and Jacek Krzaczkowski 
01.01.2021 16:15 Krzysztof Turowski 
Informatyka Teoretyczna Degree Distribution of Dynamic Graphs Generated by a DuplicationDivergence Models 
We analyze the structure of dynamic graphs generated from duplication models in which a new vertex selects an existing vertex and copies some of its neighbors and then we add some random divergence. We analyze various graph parameters like mean degree, number of open triangles, number of triangles, number of vertices of degree k or maximum degree in a graph generated from such models. We provide asymptotic analysis of expected values and tail behavior of these parameters. We also point to further extensions of this approach towards computing symmetries in these graphs and algorithms for graph compression.

13.01.2021 12:14 Maciej Nemś 
Podstawy Informatyki Regular Matching and Inclusion on Compressed Tree Patterns with Context Variables by Iovka Boneva, Joachim Niehren, and Momar Sakho 
We study the complexity of regular matching and inclusion for compressed tree patterns extended by context variables. The addition of context variables to tree patterns permits us to properly capture compressed string patterns but also compressed patterns for unranked trees with tree and hedge variables. Regular inclusion for the latter is relevant to certain query answering on Xml streams with references. 
Poprzednie referaty
19.11.2020 14:15 Łukasz Selwa, Juliusz Wajgelt 
Algorytmika Compact Distributed Certification of Planar Graphs 
18.11.2020 12:14 Michał Zwonek 
Podstawy Informatyki A Confluent Rewriting System Having No Computable, OneStep, Normalizing Strategy by JAKOB GRUE SIMONSEN 
A full and finitely generated ChurchRosser term rewriting system is presented that has no computable onestep, normalizing strategy; the system is both left and rightlinear. The result provides a negative answer to a question posed by Kennaway in 1989: Number 10 on the List of Open Problems in Rewriting. 
12.11.2020 16:15 Bartłomiej Bosek 
Optymalizacja Kombinatoryczna Harmonious Coloring of Hypergraphs 
A harmonious coloring of a kuniform hypergraph H is a vertex coloring such that no two vertices in the same edge share the same color, and each kelement subset of colors appears on at most one edge. The harmonious number h(H) is the least number of colors needed for such a coloring. We prove that kuniform hypergraphs of bounded maximum degree Δ satisfy h(H) = O(k√k!m), where m is the number of edges in H which is best possible up to a multiplicative constant. Moreover, for every fixed Δ, this constant tends to 1 with k → ∞. We use a novel method, called entropy compression, that emerged from the algorithmic version of the Lovász Local Lemma due to Moser and Tardos. This is joint work with Sebastian Czerwinski, Jarosław Grytczuk, and Paweł Rzazewski. (the seminar will only be online) 
12.11.2020 14:15 Dzianis Pivavarau, Dominik Wielgórski 
Algorytmika Explicit twodeletion codes with redundancy matching the existential bound 
05.11.2020 16:15 Piotr Mikołajczyk 
Optymalizacja Kombinatoryczna Polynomial algorithms for CFGs via semiring embeddings 
A few years ago M. Might et al. published somehow unusual approach to parsing contextfree grammars by using derivative operator. Later it was proven, that its worst case complexity is polynomial, putting it on a par with other classical approaches. We introduce an elegant generalization to this method by a generic algorithm parametrized with a semiring. Depending on the chosen algebra we can obtain polynomial algorithms for problems like parsing, recognizing or counting parse trees for CFGs.
(the seminar will only be online) 
05.11.2020 14:15 Bartłomiej Jachowicz, Mateusz Kaczmarek 
Algorytmika Counting 4Patterns in Permutations Is Equivalent to Counting 4Cycles in Graphs 
04.11.2020 12:14 Przemysław Simajchel 
Podstawy Informatyki COMPLEXITY PROBLEMS IN ENUMERATIVE COMBINATORICS by IGOR PAK 
The paper gives a broad survey of recent results in Enumerative Combinatorics and their complexity aspects. 
29.10.2020 14:15 Lech Duraj 
Algorytmika TBA 
28.10.2020 12:14 CANCELED 
Podstawy Informatyki COMPLEXITY PROBLEMS IN ENUMERATIVE COMBINATORICS by IGOR PAK 
The paper gives a broad survey of recent results in Enumerative Combinatorics and their complexity aspects. 
22.10.2020 16:15 Bartłomiej Bosek 
Optymalizacja Kombinatoryczna Conjecture 1/3  2/3 
... (the seminar will only be online) 
22.10.2020 14:15 Marcin Serwin, Wojciech Buczek 
Algorytmika A DoubleExponential Lower Bound for the Distinct Vectors Problem 
21.10.2020 12:15 Piotr Mikołajczak 
Podstawy Informatyki Asymptotic Approximation by Regular Languages by Ryoma Sin’ya 
This paper investigates a new property of formal languages called REGmeasurability where REG is the class of regular languages. Intuitively, a language L is REGmeasurable if there exists an infinite sequence of regular languages that “converges” to L. A language without REGmeasurability has a complex shape in some sense so that it can not be (asymptotically) approximated by regular languages. We show that several contextfree languages are REGmeasurable (including languages with transcendental generating function and transcendental density, in particular), while a certain simple deterministic contextfree language and the set of primitive words are REGimmeasurable in a strong sense. 
15.10.2020 16:15 Vladyslav Rachek 
Optymalizacja Kombinatoryczna Small weak epsilonnets 
Let P be a set of n points in R^{2}, ε > 0. A set of points Q is called a weak εnet for P with respect to a family S of objects (e.g. axisparallel rectangles or convex sets) if every set from S containing more than εn points of P contains a point from Q. Let R be the family of all axisparallel rectangles in R^{2} and ε^{R}_{k} be the smallest real number such that for any P there exists a weak ε^{R}_{k}net of size k. The work by Aronov et al. suggests that the inequality ε^{R}_{k} ≤ 2/(k+3) may hold. In this talk we present the complete proofs of this inequality for k=1,...,5 and prove that this bound is tight for k=1,2,3. Besides, it is not clear how to construct optimal nets. Langerman conjectured that kpoint 2/(k+3)nets can be chosen from some speciffc set of points which are the intersections of grid lines, where the grid is of size k×k. We give counterexamples to this conjecture for nets of size 3 through 6.
(the seminar will only be online) 
15.10.2020 14:15 Krzysztof Pióro, Krzysztof Potępa 
Algorytmika Modular Subset Sum 
W problemie Modular Subset Sum dane są liczba naturalna m, nelementowy multizbiór S liczb całkowitych z zakresu od 0 do m1 oraz liczba t, dla której chcemy rozstrzygnąć, czy istnieje podzbiór S, który się do niej sumuje modulo m.
Przedstawimy własne algorytmy rozwiązujące powyższy problem. Wszystkie z nich będą sprowadzały problem Modular Subset Sum do problemu tekstowego. Na początku przedstawimy prosty algorytm działający w czasie O(n + m*log^{2}(m)) wykorzystujący haszowanie i drzewa przedziałowe. Następnie pokażemy jak poprawić jego złożoność do O(n + m*log(m)). Na końcu zaprezentujemy w pełni deterministyczny wariant algorytmu działający w czasie O(n + m*log(m)*α(m)).

14.10.2020 12:15 Jędrzej Hodor 
Podstawy Informatyki Bijective link between Chapoton’s new intervals and bipartite planar maps by Wenjie Fang 
In 2006, Chapoton defined a class of Tamari intervals called “new intervals” in his enumeration of Tamari intervals, and he found that these new intervals are equienumerated with bipartite planar maps. We present here a direct bijection between these two classes of objects using a new object called “degree tree”. Our bijection also gives an intuitive proof of an unpublished equidistribution result of some statistics on new intervals given by Chapoton and Fusy. 
08.10.2020 16:15 Bartłomiej Bosek 
Optymalizacja Kombinatoryczna From the 123 Conjecture to the Riemann Hypothesis 
A series of open (and solved) problems will be presented at the seminar, starting with the 123 Conjecture and ending with the Riemann Hypothesis. (the seminar will only be online) 
08.10.2020 12:00 Patryk Mikos 
Informatyka Teoretyczna Geometric and weight constraints in Online Interval Coloring 
PhD defense  room 0004 
10.06.2020 17:00 Bartosz Wodziński 
Optymalizacja Kombinatoryczna On the unique games conjecture 
For many hard problems, instead of solving them directly, we need good approximation algorithms. Apart from good their time complexity and decent approximation factor guarantee, we would like to know whether they achieve the best possible approximation ratio (assuming P ≠ NP) possible. Unfortunately, for many NPcomplete problems, there is a huge gap between bestknown approximation ratio and the ratio that is proved to be unachievable in polynomial time. For instance, for Vertex Cover problem, we don't know any algorithm having a better ratio than 2, and it has been proved in 2005 that it is impossible to get a better ratio than ~1.36. As an attempt to fill in this gap, in 2002, the socalled Unique Games Conjecture was formulated by Khot. It states that having a (1𝜀)satisfiable instance of Unique Label Cover problem, it is NPhard to find a solution satisfying even epsilon fraction of constraints. Assuming it, we are able to prove many tight inapproximability results, for example, it implies that GoemansWilliamson Algorithm for MaxCut problem achieves the best possible approximation rate. It also follows that we cannot get any better ratio than 2 in the case of Vertex Cover problem. The Unique Games Conjecture is an unusual open problem since the academic world is about evenly divided on whether it is true or not. During the seminar, I will cover this conjecture in more details giving more examples of its influence and presenting recent progress in order to prove it.
(the seminar will only be online) 
10.06.2020 16:15 Gabriela Czarska 
Optymalizacja Kombinatoryczna The Lonely Runner Conjecture 
Abstract. Suppose that k runners having different constant speeds run laps on a circular track of unit length. The Lonely Runner Conjecture states that, sooner or later, any given runner will be at distance at least 1/k from all the other runners. We prove that with probability tending to one, a much stronger statement holds for random sets in which the bound 1/k is replaced by 1/2 − ε. The proof uses Fourier analytic methods. We also point out some consequences of our result for colouring of random integer distance graphs. (the seminar will only be online) 
10.06.2020 12:15 Wojciech Grabis 
Podstawy Informatyki Decidability of regular language genus computation by Guillaume Bonfante and Florian L. Deloup 
This article continues the study of the genus of regular languages that the authors introduced in a 2013 paper (published in 2018). In order to understand further the genus g(L) of a regular language L, we introduce the genus size of L_gen to be the minimal size of all finite deterministic automata of genus g(L) computing L.We show that the minimal finite deterministic automaton of a regular language can be arbitrarily far away from a finite deterministic automaton realizing the minimal genus and computing the same language, in terms of both the difference of genera and the difference in size. In particular, we show that the genus size Lgen can grow at least exponentially in size L. We conjecture, however, the genus of every regular language to be computable. This conjecture implies in particular that the planarity of a regular language is decidable, a question asked in 1976 by R. V. Book and A. K. Chandra. We prove here the conjecture for a fairly generic class of regular languages having no short cycles. The methods developed for the proof are used to produce new genusbased hierarchies of regular languages and in particular, we show a new family of regular languages on a twoletter alphabet having arbitrary high genus. 
10.06.2020 12:15 Wojciech Grabis 
Decidability of regular language genus computation by Guillaume Bonfante and Florian L. Deloup 
This article continues the study of the genus of regular languages that the authors introduced in a 2013 paper (published in 2018). In order to understand further the genus g(L) of a regular language L, we introduce the genus size of Lgen to be the minimal size of all finite deterministic automata of genus g(L) computing L.We show that the minimal finite deterministic automaton of a regular language can be arbitrarily far away from a finite deterministic automaton realizing the minimal genus and computing the same language, in terms of both the difference of genera and the difference in size. In particular, we show that the genus size Lgen can grow at least exponentially in size L. We conjecture, however, the genus of every regular language to be computable. This conjecture implies in particular that the planarity of a regular language is decidable, a question asked in 1976 by R. V. Book and A. K. Chandra. We prove here the conjecture for a fairly generic class of regular languages having no short cycles. The methods developed for the proof are used to produce new genusbased hierarchies of regular languages and in particular, we show a new family of regular languages on a twoletter alphabet having arbitrary high genus. 
10.06.2020 12:15 Wojciech Grabis 
Decidability of regular language genus computation by Guillaume Bonfante and Florian L. Deloup 
This article continues the study of the genus of regular languages that the authors introduced in a 2013 paper (published in 2018). In order to understand further the genus g(L) of a regular language L, we introduce the genus size of L_gen to be the minimal size of all finite deterministic automata of genus g(L) computing L. We show that the minimal finite deterministic automaton of a regular language can be arbitrarily far away from a finite deterministic automaton realizing the minimal genus and computing the same language, in terms of both the difference of genera and the difference in size. In particular, we show that the genus size L_gen can grow at least exponentially in size L. We conjecture, however, the genus of every regular language to be computable. This conjecture implies in particular that the planarity of a regular language is decidable, a question asked in 1976 by R. V. Book and A. K. Chandra. We prove here the conjecture for a fairly generic class of regular languages having no short cycles. The methods developed for the proof are used to produce new genusbased hierarchies of regular languages and in particular, we show a new family of regular languages on a twoletter alphabet having arbitrary high genus. 
10.06.2020 12:15 Wojciech Grabis 
Decidability of regular language genus computation by Guillaume Bonfante and Florian L. Deloup 
This article continues the study of the genus of regular languages that the authors introduced in a 2013 paper (published in 2018). In order to understand further the genus g(L) of a regular language L, we introduce the genus size of Lgen to be the minimal size of all finite deterministic automata of genus g(L) computing L.We show that the minimal finite deterministic automaton of a regular language can be arbitrarily far away from a finite deterministic automaton realizing the minimal genus and computing the same language, in terms of both the difference of genera and the difference in size. In particular, we show that the genus size Lgen can grow at least exponentially in size L. We conjecture, however, the genus of every regular language to be computable. This conjecture implies in particular that the planarity of a regular language is decidable, a question asked in 1976 by R. V. Book and A. K. Chandra. We prove here the conjecture for a fairly generic class of regular languages having no short cycles. The methods developed for the proof are used to produce new genusbased hierarchies of regular languages and in particular, we show a new family of regular languages on a twoletter alphabet having arbitrary high genus. 
04.06.2020 17:00 Paweł Mader 
Optymalizacja Kombinatoryczna Oblivious routing on 2d grid 
Oblivious routing is a routing problem, in which a packet path is selected independently from path choices of other packets. One of the open problems is to find networks for which there exists an oblivious routing algorithm, which allows simultaneously optimizing stretch and congestion of the network. We are presenting an algorithm for oblivious routing on 2dgrid, which is O(log n) approximation for congestion and Θ(1) approximation of stretch. (the seminar will only be online) 
04.06.2020 16:15 Raja L'hamri Mohammed V University 
Optymalizacja Kombinatoryczna Examples of codes from zerodivisor graphs 
In 2013, Dankelmann, Key, and Rodrigues introduced and investigated codes from incidence matrices of a graph. Several authors have been developed their study to several context. In this talk, we present some properties of codes associated with zero divisor graphs. Recall, the zero divisor graph of R denoted by Γ(R), is the simple graph associated with R whose set of vertices consists of all nonzero zerodivisors of R such that two distinct vertices x and y are joined by an edge if xy = 0. This is joint work with K. Abdelmoumen, D. Bennis, and F. Taraza.
(the seminar will only be online) 
03.06.2020 12:15 Ruslan Yevdokymov 
Podstawy Informatyki Learnability can be undecidable by Shai BenDavid, Pavel Hrubes, Shay Moran, Amir Shpilka and Amir Yehudayoff 
The mathematical foundations of machine learning play a key role in the development of the field. They improve our understanding and provide tools for designing new learning paradigms. The advantages of mathematics, however, sometimes come with a cost. Gödel and Cohen showed, in a nutshell, that not everything is provable. Here we show that machine learning shares this fate. We describe simple scenarios where learnability cannot be proved nor refuted using the standard axioms of mathematics. Our proof is based on the fact the continuum hypothesis cannot be proved nor refuted. We show that, in some cases, a solution to the ‘estimating the maximum’ problem is equivalent to the continuum hypothesis. The main idea is to prove an equivalence between learnability and compression. 
28.05.2020 17:00 Michał Stobierski 
Optymalizacja Kombinatoryczna The 123 Conjecture 
We all know how important mathematical theorems are in general. Less obvious is the fact that theorems in one area like algebra or number theory could have a significant impact on another. In our case, these will be combinatorial problems. In this presentation, We will go through a few simple graph coloring questions (based on the original 123 Conjecture), which unfortunately don't have simple solutions at all and we'll classify them. Moreover, thanks to Combinatorial Nullstellensatz and some greedy techniques, we will be able to prove some weaker versions of our original claims. And finally, we will see how one simple question, through a chain of small modifications, can lead us to completely different problems. (the seminar will only be online) 
28.05.2020 16:15 Rafał Byczek 
Optymalizacja Kombinatoryczna Wegner’s conjecture  colouring the square of a planar graph 
The square G^{2} of a graph G is the graph with the same vertex set in which two vertices are joined by an edge if their distance in G is at most two. The chromatic number of the square of a graph G is between D + 1 and D^{2 }+ 1, where D is the maximum degree of G. Equivalently, the square coloring of a graph is to color the vertices of a graph at distance at most 2 with different colors. In 1977, Gerd Wegner proved that the square of cubic planar graphs is 8colorable. He conjectured that his bound can be improved  the chromatic number of G^{2} is at most 7, if D = 3, at most D + 5, if 4 ≤ D ≤ 7, and [3D / 2] + 1, otherwise. Wegner also gave some examples to illustrate that these upper bounds can be obtained. C. Thomassen (2006) proved the conjecture is true for planar graphs with D = 3. The conjecture is still open for planar graphs with D ≥ 4. However several upper bounds in terms of maximum degree D have been proved as follows. In 1993, Jonas proved that χ(G^{2}) ≤ 9D19, for planar graphs with D ≥ 5. Agnarsson and Halldorson showed that for every planar graph G with maximum degree D ≥ 749, χ(G^{2}) ≤ [9D / 5] + 2. Van den Heuvel and McGuinness (2003) showed that χ(G^{2}) ≤ 2D + 25, Bordin (2002) proved that χ(G^{2}) ≤ [9D / 5] + 1, if D ≥ 47, and Molloy and Salavatipour (2005) proved χ(G^{2}) ≤ [5D / 3] + 78, moreover, χ(G^{2}) ≤ [5D / 3] + 25 if D ≥ 241. Moreover, conjecture is confirmed in the case of outerplanar graphs and graphs without K_{4} minor. The aim of the seminar will be to present the main facts about Wegner’s conjecture and main techniques and ideas which were used to prove some upper bounds. The presentation will be based on my master thesis. (the seminar will only be online) 
27.05.2020 12:00 Szymaon Kapała 
Podstawy Informatyki Searching for shortest and least programs by Cristian Caludea, Sanjay Jain, Wolfgang Merkle and Frank Stephan 
The Kolmogorov complexity of a string x is defined as the length of a shortest program p of x for some appropriate universal machine U, that is, U(p) =x and p is a shortest string with this property. Neither the plain nor the prefixfree version of Kolmogorov complexity are recursive but for both versions it is wellknown that there are recursive exact Solovay functions, that is, recursive upper bounds for Kolmogorov complexity that are infinitely often tight. Let a coding function for a machine M be a function f such that f(x) is always a program of x for M. From the existence of exact Solovay functions it follows easily that for every universal machine there is a recursive coding function that maps infinitely many strings to a shortest program. Extending a recent line of research, in what follows it is investigated in which situations there is a coding function for some universal machine that maps infinitely many strings to the lengthlexicographically least program. The main results which hold in the plain as well as in the prefixfree setting are the following. For every universal machine there is a recursive coding function that maps infinitely many strings to their least programs. There is a partial recursive coding function (defined in the natural way) for some universal machine that for every set maps infinitely many prefixes of the set to their least programs. Exactly for every set that is Bennett shallow (not deep), there is a recursive coding function for some universal machine that maps all prefixes of the set to their least programs. Differences between the plain and the prefixfree frameworks are obtained by considering effective sequences I_1, I_2, ...of mutually disjoint finite sets and asking for a recursive coding function for some universal machine that maps at least one string in each set I_n to its least code. Such coding functions do not exist in the prefixfree setting but exist in the plain setting in case the sets I_n are not too small. 
21.05.2020 16:15 Wojtek Grabis 
Optymalizacja Kombinatoryczna Algorithms for Destructive Shift Bribery. 
Destructive Shift Bribery is a problem in which we are given an election with a set of candidates and a set of voters, a budget , a despised candidate and price for shifting the despised candidate in the voters rankings. Our objective is to ensure that selected candidate cannot win the election. We're going to study the complexity of this problem under diffrent election methods.
(the seminar will only be online) 
20.05.2020 12:15 Piotr Mikołajczyk 
Podstawy Informatyki Lambda Calculus and Probabilistic Computation by Claudia Faggian and Simona Ronchi della Rocca 
We introduce two extensions of the lambda calculus with a probabilistic choice operators, modeling respectively callbyvalue and callbyname probabilistic computation. We prove that both enjoys confluence and standardization, in an extended way: we revisit these two fundamental notions to take into account the asymptotic behaviour of terms. The common root of the two calculi is a further calculus based on Linear Logic ! which allows us to develop a unified, modular approach. 
14.05.2020 17:00 Jan Mełech 
Optymalizacja Kombinatoryczna Upper Bounds for the domination numbers of graphs 
Sharareh Alipour and Amir Jafari showed various upper bounds for minimal cardinality of (a,b)dominating set. For positive integers a and b, a subset S ⊆ V(G) is an (a,b)dominating set if every vertex v ∈ S is adjacent to at least a vertices inside S and every vertex v ∈ V\S is adjacent to at least b vertices inside S. To achieve upper bounds, the authors used Turan's Theorem and Lovasz Local Lemma. These tools allowed them to obtain wellknown bounds in a simpler way or new improved bounds in some special cases, including regular graphs.
(the seminar will only be online) 
14.05.2020 16:15 Szymon Kapała 
Optymalizacja Kombinatoryczna Goldbach conjectures (weak and strong). 
(the seminar will only be online) 
13.05.2020 12:15 Przemysław Simajchel 
Podstawy Informatyki Dance of the Starlings by Henk Barendregt, Jorg Endrullis, Jan Klop and Johannes Waldmann 
In this birdwatching paper our binoculars are focused upon a particular bird from Smullyan's enchanted forest of combinatory birds, to wit the Starling. In the feathers of lambda calculus this bird has the plumage \abc:ac(bc). This term is usually named S, reminiscent of its inventor Schonfinkel and also the combinatory ornithologist Smullyan. The combinator S is important for a variety of reasons. First, it is part of the \{ S, K\} basis for Combinatory Logic (CL). Second, there are several interesting questions and observations around S, mostly referring to termination and word problems. Our paper collects known facts, but poses in addition several new questions. For some of these we provide solutions, but several tough open questions remain. 
07.05.2020 16:15 Michał Zwonek 
Optymalizacja Kombinatoryczna 3flow conjecture 
3flowconjecture Grötzsch proved that every triangle free (and loopless) planar graph is 3colorable. By flow/coloring duality, this is equivalent to the statement that every 4edgeconnected planar graph has a nowherezero 3flow. The 3flow conjecture asserts that this is still true without the assumption of planarity. Jaeger proved that 4edgeconnected graphs have nowherezero 4flows. The following weak version of the 3flow conjecture used to remain open until 2010, but the original 3flow conjecture remains wide open. C̶o̶n̶j̶e̶c̶t̶u̶r̶e̶ (The weak 3flow conjecture (Jaeger)) These problems and the surrounding results will be presented during the seminar.
(the seminar will only be online) 
06.05.2020 12:15 Bartłomiej Puget 
Podstawy Informatyki Evidence Normalization in System FC by Dimitrios Vytiniotis and Simon Peyton Jones 
System FC is an explicitly typed language that serves as the target language for Haskell source programs. System FC is based on System F with the addition of erasable but explicit type equality proof witnesses. Equality proof witnesses are generated from type inference performed on source Haskell programs. Such witnesses may be very large objects, which causes performance degradation in later stages of compilation, and makes it hard to debug the results of type inference and subsequent program transformations. In this paper, we present an equality proof simplification algorithm, implemented in GHC, which greatly reduces the size of the target System FC programs. 
30.04.2020 17:00 Mateusz Kaczmarek 
Optymalizacja Kombinatoryczna χboundedness 
If a graph has bounded clique number and sufficiently large chromatic number, what can we say about its induced subgraphs? To answer that question Paul Seymour and Alex Scott took a closer look at recent progress in this field in their χboundedness survey. Based on their work I will present some results on forests and holes and few open problems like GyárfásSumner conjecture or χboundedness connection to ErdősHajnal conjecture.
(the seminar will only be online) 
30.04.2020 16:15 Kornel Dulęba 
Optymalizacja Kombinatoryczna Odd Perfect numbers 
A number is perfect if it is equal to the sum of its divisors. So far only even perfect numbers have been found. For example, it was proven that squares of Mersenne’s numbers are perfect. However, no one has been able to prove that odd perfect numbers don’t exist. I’m going to start by presenting a summary of known facts about odd prime numbers. Then I’ll prove that an odd perfect number with at least eight distinct prime factors has to be divisible by 5.
(the seminar will only be online) 
29.04.2020 12:15 Jakub Dyczek 
Podstawy Informatyki On probabilistic term rewriting by Martin Avanzinia,Ugo Dal Lago and Akihisa Yamadac 
We study the termination problem for probabilistic term rewrite systems. We prove that the interpretation method is sound and complete for a strengthening of positive almost sure termination, when abstract reduction systems and term rewrite systems are considered. Two instances of the interpretation method polynomial and matrix interpretations are analyzed and shown to capture interesting and nontrivial examples when automated. We capture probabilistic computation in a novel way by means of multidistribution reduction sequences, thus accounting for both the nondeterminism in the choice of the redex and the probabilism intrinsic in firing each rule. 
23.04.2020 17:00 Bartłomiej Jachowicz 
Optymalizacja Kombinatoryczna Lonely runner conjecture 
One of number theory open problem is the Lonely Runner Conjecture. It is interesting for several reasons. First the conjecture is relatively intuitive to grasp and easy to state. This conjecture can be find in two different contexts: as a problem in Diophantine’s approximation and as a geometric view obstruction problem. What is more, the difficulty of proving the Lonely Runner Conjecture may seem to increase exponentially with the number of runners. I present statement of the conjecture and known partial results.
(the seminar will only be online) 
23.04.2020 16:15 Filip Bartodziej 
Optymalizacja Kombinatoryczna Meyniel’s conjecture on the cop number 
A cops and robbers problem determines if the number of cops is sufficient to always catch a robber in a game with defined rules played on an undirected graph. Cop number of a graph is the minimal number of cops necessary for cops to win in that game on the specific graph. Mayniel’s conjuncture remains an open problem and states that cop number for graphs of order n is sqrt(n). I’ll present a survey of results achieved that are related to this conjecture.
(the seminar will only be online) 
22.04.2020 12:15 Jan Kościsz 
Podstawy Informatyki Fast Synchronization of Random Automata by Cyril Nicaud 
A synchronizing word for an automaton is a word that brings that automaton into one and the same state, regardless of the starting position. Cerný conjectured in 1964 that if a nstate deterministic automaton has a synchronizing word, then it has a synchronizing word of length at most (n − 1)^2. Berlinkov recently made a breakthrough in the probabilistic analysis of synchronization: he proved that, for the uniform distribution on deterministic automata with n states, an automaton admits a synchronizing word with high probability. In this article, we are interested in the typical length of the smallest synchronizing word, when such a word exists: we prove that a random automaton admits a synchronizing word of length O(n log^3 n) with high probability. As a consequence, this proves that most automata satisfy the Cerný conjecture. 
16.04.2020 17:00 Mateusz Pabian 
Optymalizacja Kombinatoryczna Synchronizing Automata and the Černý Conjecture 
I present many results and finally open problem related to synchronizing automata and synchronizing word sends any state of the DFA to one and the same state. This leads to the some natural problems such as: how can we restore control over such a device if we don't know its current state but can observe outputs produced by the device under various actions? I prove some uperbounds for length of this kind of word and in particular I will make a statement of Cerny conjecture.
(the seminar will only be online) 
16.04.2020 16:15 Adrian Siwiec 
Optymalizacja Kombinatoryczna Online Computation with Untrusted Advice 
The advice model of online computation captures the setting in which the online algorithm is given some partial information concerning the request sequence. We study online computation in a setting in which the advice is provided by an untrusted source. Our objective is to quantify the impact of untrusted advice so as to design and analyze online algorithms that are robust and perform well even when the advice is generated in a malicious, adversarial manner.To this end, we focus on wellstudied online problems such as ski rental, online bidding, bin packing, and list update.
(the seminar will only be online) 
15.04.2020 12:15 Magdalena Proszewska 
Podstawy Informatyki Singular value automata and approximate minimization by Borja Balle, Prakash Panangaden and Doina Precup 
The present paper uses spectral theory of linear operators to construct approximately minimal realizations of weighted languages. Our new contributions are: (i) a new algorithm for the singular value decomposition (SVD) decomposition of finiterank infinite Hankel matrices based on their representation in terms of weighted automata, (ii) a new canonical form for weighted automata arising from the SVD of its corresponding Hankelmatrix, and (iii) an algorithm to construct approximate minimizations of given weighted automata by truncating the canonical form. We give bounds on the quality of our approximation. 
09.04.2020 17:00 Wojciech Buczek 
Optymalizacja Kombinatoryczna Seymour's Second Neighbourhood Conjecture 
Seymour's Second Neighbourhood Conjecture tells us, that any oriented graph has a vertex whose outdegree is at most its second outdegree, which is also known as Second neighborhood problem. Intuitively, it suggests that in a social network described by such a graph, someone will have at least as many friendsoffriends as friends. We will say about ChenShenYuster prove, that for any digraph D, there exists a vertex v such that N^{++}(v)≥γN^{+}(v), where γ=0.67815. We will consider graphs, in which we know, that such vertex exists. We will also say about unsuccessful attempts at proving this conjecture.
(the seminar will only be online) 
09.04.2020 16:15 Mikołaj Twaróg 
Optymalizacja Kombinatoryczna Collatz conjecture 
The Collatz conjecture, also known as 3n + 1 conjecture considers a function, which returns n/2 if n is even and 3n + 1 if n is odd. The conjecture states that for every n we can repeatedly apply this function to eventually reach 1. I will talk about different approaches to proving this conjecture. (the seminar will only be online) 
08.04.2020 12:15 Jacek Kurek 
Podstawy Informatyki Complexity of translations from resolution to sequent calculus by GISELLE REIS and BRUNO PALEO 
Resolution and sequent calculus are two wellknown formal proof systems. Their differences make them suitable for distinct tasks. Resolution and its variants are very efficient for automated reasoning and are in fact the theoretical basis of many theorem provers. However, being intentionally machine oriented, the resolution calculus is not as natural for human beings and the input problem needs to be preprocessed to clause normal form. Sequent calculus, on the other hand, is a modular formalism that is useful for analysing metaproperties of various logics and is, therefore, popular among proof theorists. The input problem does not need to be preprocessed, and proofs are more detailed. However, proofs also tend to be larger and more verbose. When the worlds of proof theory and automated theorem proving meet, translations between resolution and sequent calculus are often necessary. In this paper, we compare three translation methods and analyse their complexity. 
02.04.2020 17:00 Adam Pardyl 
Optymalizacja Kombinatoryczna Undirected edge geography 
The game of edge geography is played by two players who alternately move a token on a graph from one vertex to an adjacent vertex, erasing the edge in between. The player who first has no legal move loses the game. We analyze the space complexity of the decision problem of determining whether a start position in this game is a win for the first player. We also show a polynomial time algorithm for finding winning moves for bipartite graphs.
(the seminar will only be online) 
02.04.2020 16:15 Piotr Mikołajczyk 
Optymalizacja Kombinatoryczna ARRIVAL game 
Consider a directed graph such that every vertex has at most 2 outgoing edges  one of them is labeled as 'open' (we can traverse it) and the second one is labeled as 'closed' (we cannot traverse it). Every time we go somewhere from the vertex v, labels at its two edges are swapped, so the next time we visit v, we will take another direction. Given designated two vertices: origin and destination, we need to decide, whether eventually we will reach destination starting in the origin. This problem lies in both NP and coNP, but it is still an open question whether it belongs to P.
(the seminar will only be online) 
01.04.2020 12:15 Rafał Byczek 
Podstawy Informatyki Bijection between oriented maps and weighted nonoriented maps by Agnieszka CzyzewskaJankowska and Piotr Śniady 
We consider bicolored maps, i.e. graphs which are drawn on surfaces, and construct a bijection between (i) oriented maps with arbitrary face structure, and (ii) (weighted) nonoriented maps with exactly one face. Above, each non oriented map is counted with a multiplicity which is based on the concept of the orientability generating series and the measure of orientability of a map. This bijection has the remarkable property of preserving the underlying bicolored graph. Our bijection shows equivalence between two explicit formulas for the topdegree of Jack characters, i.e. (suitably normalized) coefficients in the expansion of Jack symmetric functions in the basis of powersum symmetric functions. 
26.03.2020 16:15 Vladyslav Rachek 
Optymalizacja Kombinatoryczna Small weak epsilonnets 
Let P be a set of n points in R^{2}. A point q (not necessarily in P) is called a centerpoint of P if each closed halfplane containing q at least ⌈n/3⌉ points of P, or, equivalently, any convex set that contains more than ^{2}/_{3 }n points of P must also contain q. It is a wellknown fact that a centerpoint always exists and the constant ^{2}/_{3} is the best possible. Can we improve this constant by using, say, two points, or some other small number of points? In the presentation we'll try to answer those questions. Vladyslav Rachek. Small weak epsilonnets. slides. 2020. (the seminar will only be online) 
25.03.2020 12:15 Michał Zwonek 
Podstawy Informatyki FUNCTIONAL PEARL How to find a fake coin by RICHARD BIRD 
The aim of this pearl is to solve the following wellknown problem that appears in many puzzle books, for example Levitin & Levitin (2011) and Bellos (2016), usually for the particular case n=12.

19.03.2020 17:00 Kamil Rajtar 
Optymalizacja Kombinatoryczna How voting can be manipulated during selecting voting places 
During today presentation we will learn how we can use graph theory to proof hardness of general problem of manipulating poll outcome. Based on paper: "Selecting Voting Locations for Fun and Profit" written by Zack Fitzsimmons and Omer Lev. Zack Fitzsimmons, Omer Lev. Selecting Voting Locations for Fun and Profit. arXiv:2003.06879. 2020. (the seminar will only be online) 
19.03.2020 16:15 Mateusz Tokarz 
Optymalizacja Kombinatoryczna The HadwigerNelson problem 
We will focus on HadwigerNelson problem  an open question from geometric graph theory that asks for the minimum number of colors required to color the plane such that no two points at distance 1 from each other have the same color. There are a few interesting theorems related to the problem and results which we will go through. We will focus in particular on the most recent result of Aubrey de Grey who showed that the desired chromatic number is at least 5.
(the seminar will only be online) 
18.03.2020 12:15 Mateusz Tokarz, wyniki własne, kontynuacja 
Podstawy Informatyki The largest fixed point in iterative programs 
We study the smallest ordinal number α such that every Prologue program will reach its greatest fixed point after α downward iterations. Firstly, we show that the continuity of Prologue’s resolution function does not help with this matter. Then, due to the embedding of the recursive functions in Prologue, we get that α is at least ChurchKleene Omega. Using recursive linear order presented in “On the Forms of the Predicates in the Theory of Constructive Ordinals“ (Kleene, 1944) we construct a Prologue’s program requiring at least CK Omega steps to achieve its greatest fixed point. To get the upper bound on α we use clockable ordinals introduced in “Infinite Time Turing Machines” (Joel David Hamkins, Andy Lewis, 1998). 
11.03.2020 12:15 Mateusz Tokarz wyniki własne 
Podstawy Informatyki The largest fixed point in iterative programs 
We study the smallest ordinal number α such that every Prologue program will reach its greatest fixed point after α downward iterations. Firstly, we show that the continuity of Prologue’s resolution function does not help with this matter. Then, due to the embedding of the recursive functions in Prologue, we get that α is at least ChurchKleene Omega. Using recursive linear order presented in “On the Forms of the Predicates in the Theory of Constructive Ordinals“ (Kleene, 1944) we construct a Prologue’s program requiring at least CK Omega steps to achieve its greatest fixed point. To get the upper bound on α we use clockable ordinals introduced in “Infinite Time Turing Machines” (Joel David Hamkins, Andy Lewis, 1998). 
23.01.2020 16:15 Jan Gwinner 
Optymalizacja Kombinatoryczna Spectrally Robust Graph Isomorphism 
In the paper authors consider certain variants of Graph Isomorphism problem. They focus on properties of graph spectra and eigenspaces  namely if Laplacian of one of the graphs is greater or equal to another in Loewner ordering. In the first part of the paper they prove that one of the problems named Spectral Graph Dominance is NPC. The rest of the paper is devoted to an approximation algorithm for special case of the problem called Spectrally Robust Graph Isomorphism. 
22.01.2020 12:15 Weronika Grzybowska i Mateusz Tokarz 
Podstawy Informatyki On two subclasses of Motzkin paths and their relation to ternary trees by Helmut Prodinger, Sarah J. Selkirk and Stephan Wagner 
Two subclasses of Motzkin paths, SMotzkin and TMotzkin paths, are introduced. We provide bijections between SMotzkin paths and ternary trees, SMotzkin paths and noncrossing trees, and TMotzkin paths and ordered pairs of ternary trees. Symbolic equations for both paths, and thus generating functions for the paths, are provided. Using these, various parameters involving the two paths are analyzed. 
16.01.2020 17:00 Gabriela Czarska 
Optymalizacja Kombinatoryczna Driver surge pricing 
Authors study Uber's pricing mechanisms from the perspective of drivers, presenting the theoretical foundation that has informed the design of Uber’s new additive driver surge mechanism. They present a dynamic stochastic model to capture the impact of surge pricing on driver earnings and their strategies to maximize such earnings. Nikhil Garg, Hamid Nazerzadeh. Driver Surge Pricing. arXiv. 2019. 
16.01.2020 16:15 Bartosz Podkanowicz 
Optymalizacja Kombinatoryczna Planar graphs have bounded queuenumber 
The paper presents proof that the queue number of planar graphs is bounded. It also mentions generalizations of the result and other theorems that have similar proofs. 
16.01.2020 14:15 Katarzyna Król, Paweł Mader 
Algorytmika On the Complexity of Lattice Puzzles [Kobayashi et al.] 
Autorzy pracy badają złożoność obliczeniową tradycyjnej łamigłówki zwaną dalej układanką kratową. Celem układanki jest złożenie kraty o wymiarach n×n z 2n płytek z szczelinami. Łamigówka ta jest powszechnie znanym problemem, niemniej jednak do tej pory nie była ona badana przez informatykę teoretyczną. Autorzy pracy pokazują, że naturalne warianty tej układanki redukują się do podklas w klasie złożoności NP. Jedną z takich podklas jest klasa problemu izomorfizmów grafów GI. O ile wiadomo autorom pracy, jest to pierwszy nietrywialny GIzupełny problem scharakteryzowany przez klasyczną łamigłówkę. 
15.01.2020 16:15 Michał Seweryn 
Informatyka Teoretyczna ErdösHajnal properties for powers of sparse graphs 
The notion of nowhere dense classes of graphs attracted much attention in recent years and found many applications in structural graph theory and algorithmics. The powers of nowhere dense graphs do not need to be sparse, for instance the second power of star graphs are complete graphs. However, it is believed that powers of sparse graphs inherit somewhat simple structure. In this spirit, we show that for a fixed nowhere dense class of graphs, a positive real ε and a positive integer d, in any nvertex graph G in the class, there are disjoint vertex subsets A and B with A=Ω(n) and B=Ω(n^{1ε}) such that in the dth power of G, either there is no edge between A and B, or there are all possible edges between A and B.
Joint work with Marcin Briański, Piotr Micek and Michał Pilipczuk 
15.01.2020 12:15 Wojciech Grabis 
Podstawy Informatyki Ant colony optimization theory: A survey by Marco Dorigoa and Christian Blumb 
Research on a new metaheuristic for optimization is often initially focused on proofofconcept applications. It is only after experimental work has shown the practical interest of the method that researchers try to deepen their understanding of the method’s functioning not only through more and more sophisticated experiments but also by means of an effort to build a theory. Tackling questions such as “how and why the method works’’ is important, because finding an answer may help in improving its applicability. Ant colony optimization, which was introduced in the early 1990s as a novel technique for solving hard combinatorial optimization problems, finds itself currently at this point of its life cycle. With this article we provide a survey on theoretical results on ant colony optimization. First, we reviewsome convergence results. Then we discuss relations between ant colony optimization algorithms and other approximate methods for optimization. Finally, we focus on some research efforts directed at gaining a deeper understanding of the behavior of ant colony optimization algorithms. Throughout the paper we identify some open questions with a certain interest of being solved in the near future. 
09.01.2020 17:00 Wojtek Grabis 
Optymalizacja Kombinatoryczna Algorithms for Destructive Shift Bribery. 
Destructive Shift Bribery is a problem in which we are given an election with a set of candidates and a set of voters, a budget , a despised candidate and price for shifting the despised candidate in the voters rankings. Our objective is to ensure that selected candidate cannot win the election. We're going to study the complexity of this problem under diffrent election methods. Andrzej Kaczmarczyk, Piotr Faliszewski. Algorithms for Destructive Shift Bribery. arXiv. 2018. 
09.01.2020 16:15 Dominik Gryboś 
Optymalizacja Kombinatoryczna Imperfect Forward Secrecy: How DiffieHellman Fails in Practice 
The paper shows that the DiffieHellman protocol is not as secure as we thought. The authors present the Logjam attack, which consists in quickly calculating discrete logarithms based on previously performed calculations. This can be done because many websites use the same prime numbers in the message encryption process. 
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