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Extremal Problems For Finite Sets
''Extremal Problems For Finite Sets'' is a mathematics book on the extremal combinatorics of finite sets and families of finite sets. It was written by Péter Frankl and Norihide Tokushige, and published in 2018 by the American Mathematical Society as volume 86 of their Student Mathematical Library book series. The Basic Library List Committee of the Mathematical Association of America has suggested its inclusion in undergraduate mathematics libraries. Topics The book has 32 chapters. Its topics include: *Sperner's theorem, on the largest antichain in the family of subsets of a given finite set. *The Sauer–Shelah lemma, on the largest size of a family of sets that avoids shattering any set of given size. *The Erdős–Ko–Rado theorem, on the largest pairwise-intersecting family of subsets of a given finite set, with multiple proofs; the closely related Lubell–Yamamoto–Meshalkin inequality; the Hilton-Milner theorem, on the largest intersecting family with no element in c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Extremal Problems For Finite Sets
''Extremal Problems For Finite Sets'' is a mathematics book on the extremal combinatorics of finite sets and families of finite sets. It was written by Péter Frankl and Norihide Tokushige, and published in 2018 by the American Mathematical Society as volume 86 of their Student Mathematical Library book series. The Basic Library List Committee of the Mathematical Association of America has suggested its inclusion in undergraduate mathematics libraries. Topics The book has 32 chapters. Its topics include: *Sperner's theorem, on the largest antichain in the family of subsets of a given finite set. *The Sauer–Shelah lemma, on the largest size of a family of sets that avoids shattering any set of given size. *The Erdős–Ko–Rado theorem, on the largest pairwise-intersecting family of subsets of a given finite set, with multiple proofs; the closely related Lubell–Yamamoto–Meshalkin inequality; the Hilton-Milner theorem, on the largest intersecting family with no element in c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Václav Chvátal
Václav (Vašek) Chvátal () is a Professor Emeritus in the Department of Computer Science and Software Engineering at Concordia University in Montreal, Quebec, Canada and a Visiting Professor at Charles University in Prague. He has published extensively on topics in graph theory, combinatorics, and combinatorial optimization. Biography Chvátal was born in 1946 in Prague and educated in mathematics at Charles University in Prague, where he studied under the supervision of Zdeněk Hedrlín. He fled Czechoslovakia in 1968, three days after the Soviet invasion, and completed his Ph.D. in Mathematics at the University of Waterloo, under the supervision of Crispin St. J. A. Nash-Williams, in the fall of 1970. Subsequently, he took positions at McGill University (1971 and 1978-1986), Stanford University (1972 and 1974-1977), the Université de Montréal (1972-1974 and 1977-1978), and Rutgers University (1986-2004) before returning to Montreal for the Canada Research Chair in Combi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mathematics Books
Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics with the major subdisciplines of number theory, algebra, geometry, and analysis, respectively. There is no general consensus among mathematicians about a common definition for their academic discipline. Most mathematical activity involves the discovery of properties of abstract objects and the use of pure reason to prove them. These objects consist of either abstractions from nature orin modern mathematicsentities that are stipulated to have certain properties, called axioms. A ''proof'' consists of a succession of applications of deductive rules to already established results. These results include previously proved theorems, axioms, andin case of abstraction from naturesome basic properties that are considered true starting points of t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Families Of Sets
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideally, families offer predictability, structure, and safety as members mature and learn to participate in the community. Historically, most human societies use family as the primary locus of attachment, nurturance, and socialization. Anthropologists classify most family organizations as matrifocal (a mother and her children), patrifocal (a father and his children), conjugal (a wife, her husband, and children, also called the nuclear family), avuncular (a man, his sister, and her children), or extended (in addition to parents and children, may include grandparents, aunts, uncles, or cousins). The field of genealogy aims to trace family lineages through history. The family is also an important economic unit studied in family economics. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Combinatorics
Combinatorics is an area of mathematics primarily concerned with counting, both as a means and an end in obtaining results, and certain properties of finite structures. It is closely related to many other areas of mathematics and has many applications ranging from logic to statistical physics and from evolutionary biology to computer science. Combinatorics is well known for the breadth of the problems it tackles. Combinatorial problems arise in many areas of pure mathematics, notably in algebra, probability theory, topology, and geometry, as well as in its many application areas. Many combinatorial questions have historically been considered in isolation, giving an ''ad hoc'' solution to a problem arising in some mathematical context. In the later twentieth century, however, powerful and general theoretical methods were developed, making combinatorics into an independent branch of mathematics in its own right. One of the oldest and most accessible parts of combinatorics is gra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metric Space
In mathematics, a metric space is a set together with a notion of ''distance'' between its elements, usually called points. The distance is measured by a function called a metric or distance function. Metric spaces are the most general setting for studying many of the concepts of mathematical analysis and geometry. The most familiar example of a metric space is 3-dimensional Euclidean space with its usual notion of distance. Other well-known examples are a sphere equipped with the angular distance and the hyperbolic plane. A metric may correspond to a metaphorical, rather than physical, notion of distance: for example, the set of 100-character Unicode strings can be equipped with the Hamming distance, which measures the number of characters that need to be changed to get from one string to another. Since they are very general, metric spaces are a tool used in many different branches of mathematics. Many types of mathematical objects have a natural notion of distance and t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hypergraph
In mathematics, a hypergraph is a generalization of a graph in which an edge can join any number of vertices. In contrast, in an ordinary graph, an edge connects exactly two vertices. Formally, an undirected hypergraph H is a pair H = (X,E) where X is a set of elements called ''nodes'' or ''vertices'', and E is a set of non-empty subsets of X called ''hyperedges'' or ''edges''. Therefore, E is a subset of \mathcal(X) \setminus\, where \mathcal(X) is the power set of X. The size of the vertex set is called the ''order of the hypergraph'', and the size of edges set is the ''size of the hypergraph''. A directed hypergraph differs in that its hyperedges are not sets, but ordered pairs of subsets of X, with each pair's first and second entries constituting the tail and head of the hyperedge respectively. While graph edges connect only 2 nodes, hyperedges connect an arbitrary number of nodes. However, it is often desirable to study hypergraphs where all hyperedges have the same card ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Union-closed Sets Conjecture
The union-closed sets conjecture is an open problem in combinatorics posed by Péter Frankl in 1979. A family of sets is said to be ''union-closed'' if the union of any two sets from the family belongs to the family. The conjecture states: For every finite union-closed family of sets, other than the family containing only the empty set, there exists an element that belongs to at least half of the sets in the family. Professor Timothy Gowers has called this "''one of the best known open problems in combinatorics''" and has said that the conjecture "''feels as though it ought to be easy (and as a result has attracted a lot of false proofs over the years). A good way to understand why it isn't easy is to spend an afternoon trying to prove it. That clever averaging argument you had in mind doesn't work ...''" Example The family of sets\varnothing, \, \, \, \consists of five different sets and is union-closed. The element 1 is contained in three of the five sets (and so is the el ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sunflower (mathematics)
In the mathematical fields of set theory and extremal combinatorics, a sunflower or \Delta-system is a collection of sets whose pairwise intersection is constant. This constant intersection is called the kernel of the sunflower. The main research question arising in relation to sunflowers is: under what conditions does there exist a ''large'' sunflower (a sunflower with many sets) in a given collection of sets? The \Delta-lemma, sunflower lemma, and the Erdős-Rado sunflower conjecture give successively weaker conditions which would imply the existence of a large sunflower in a given collection, with the latter being one of the most famous open problems of extremal combinatorics. Formal definition Suppose W is a set system over U, that is, a collection of subsets of a set U. The collection W is a ''sunflower'' (or ''\Delta-system'') if there is a subset S of U such that for each distinct A and B in W, we have A \cap B = S. In other words, a set system or collection of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cap Set
In affine geometry, a cap set is a subset of \mathbb_3^n (an n-dimensional affine space over a three-element field) with no three elements in a line. The cap set problem is the problem of finding the size of the largest possible cap set, as a function of n.. The first few cap set sizes are 1, 2, 4, 9, 20, 45, 112, ... . Cap sets may be defined more generally as subsets of finite affine or projective spaces with no three in line, where these objects are simply called caps. The "cap set" terminology should be distinguished from other unrelated mathematical objects with the same name, and in particular from sets with the compact absorption property in function spaces as well as from compact convex co-convex subsets of a convex set. Example An example of cap sets comes from the card game Set, a card game in which each card has four features (its number, symbol, shading, and color), each of which can take one of three values. The cards of this game can be interpreted as representing p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kruskal–Katona Theorem
In algebraic combinatorics, the Kruskal–Katona theorem gives a complete characterization of the ''f''-vectors of abstract simplicial complexes. It includes as a special case the Erdős–Ko–Rado theorem and can be restated in terms of uniform hypergraphs. It is named after Joseph Kruskal and Gyula O. H. Katona, but has been independently discovered by several others. Statement Given two positive integers ''N'' and ''i'', there is a unique way to expand ''N'' as a sum of binomial coefficients as follows: : N=\binom+\binom+\ldots+\binom,\quad n_i > n_ > \ldots > n_j \geq j\geq 1. This expansion can be constructed by applying the greedy algorithm: set ''n''''i'' to be the maximal ''n'' such that N\geq \binom, replace ''N'' with the difference, ''i'' with ''i'' − 1, and repeat until the difference becomes zero. Define : N^=\binom+\binom+\ldots+\binom. Statement for simplicial complexes An integral vector (f_0, f_1, ..., f_) is the ''f''-vector of some (d-1)-dimen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lubell–Yamamoto–Meshalkin Inequality
In combinatorial mathematics, the Lubell–Yamamoto–Meshalkin inequality, more commonly known as the LYM inequality, is an inequality on the sizes of sets in a Sperner family, proved by , , , and . It is named for the initials of three of its discoverers. To include the initials of all four discoverers, it is sometimes referred to as the YBLM inequality. This inequality belongs to the field of combinatorics of sets, and has many applications in combinatorics. In particular, it can be used to prove Sperner's theorem. Its name is also used for similar inequalities. Statement of the theorem Let ''U'' be an ''n''-element set, let ''A'' be a family of subsets of ''U'' such that no set in ''A'' is a subset of another set in ''A'', and let ''ak'' denote the number of sets of size ''k'' in ''A''. Then : \sum_^n\frac \le 1. Lubell's proof proves the Lubell–Yamamoto–Meshalkin inequality by a double counting argument in which he counts the permutation In mathematics, a permutati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
