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Baumslag–Solitar Group
In the mathematical field of group theory, the Baumslag–Solitar groups are examples of two-generator one-relator groups that play an important role in combinatorial group theory and geometric group theory as (counter)examples and test-cases. They are given by the group presentation : \left \langle a, b \ : \ b a^m b^ = a^n \right \rangle. For each integer and , the Baumslag–Solitar group is denoted . The relation in the presentation is called the Baumslag–Solitar relation. Some of the various are well-known groups. is the free abelian group on two generators, and is the fundamental group of the Klein bottle. The groups were defined by Gilbert Baumslag and Donald Solitar in 1962 to provide examples of non- Hopfian groups. The groups contain residually finite groups, Hopfian groups that are not residually finite, and non-Hopfian groups. Linear representation Define :A= \begin1&1\\0&1\end, \qquad B= \begin\frac&0\\0&1\end. The matrix group generated by and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Klein Bottle
In topology, a branch of mathematics, the Klein bottle () is an example of a non-orientable surface; it is a two-dimensional manifold against which a system for determining a normal vector cannot be consistently defined. Informally, it is a one-sided surface which, if traveled upon, could be followed back to the point of origin while flipping the traveler upside down. Other related non-orientable objects include the Möbius strip and the real projective plane. While a Möbius strip is a surface with boundary, a Klein bottle has no boundary. For comparison, a sphere is an orientable surface with no boundary. The concept of a Klein bottle was first described in 1882 by the German mathematician Felix Klein. Construction The following square is a fundamental polygon of the Klein bottle. The idea is to 'glue' together the corresponding red and blue edges with the arrows matching, as in the diagrams below. Note that this is an "abstract" gluing in the sense that trying to realize ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Binary Tiling
In geometry, the binary tiling (sometimes called the Böröczky tiling) is a tiling of the hyperbolic plane, resembling a quadtree over the Poincaré half-plane model of the hyperbolic plane. It was first studied mathematically in 1974 by . However, a closely related tiling was used earlier in a 1957 print by M. C. Escher. See especially text describing ''Regular Division of the Plane VI'', pp. 112 & 114, schematic diagram, p. 116, and reproduction of the print, p. 117. Tiles In one version of the tiling, the tiles are shapes bounded by three congruent horocyclic segments (two of which are part of the same horocycle), and two line segments. All tiles are congruent. In the Poincaré half-plane model, the horocyclic segments are modeled as horizontal line segments (parallel to the boundary of the half-plane) and the line segments are modeled as vertical line segments (perpendicular to the boundary of the half-plane), giving each tile the overall shape in the model of a square or r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anatoly Maltsev
Anatoly Ivanovich Maltsev (also: Malcev, Mal'cev; Russian: Анато́лий Ива́нович Ма́льцев; 27 November N.S./14 November O.S. 1909, Moscow Governorate – 7 June 1967, Novosibirsk) was born in Misheronsky, near Moscow, and died in Novosibirsk, USSR. He was a mathematician noted for his work on the decidability of various algebraic groups. Malcev algebras (generalisations of Lie algebras), as well as Malcev Lie algebras are named after him. Biography At school, Maltsev demonstrated an aptitude for mathematics, and when he left school in 1927, he went to Moscow State University to study Mathematics. While he was there, he started teaching in a secondary school in Moscow. After graduating in 1931, he continued his teaching career and in 1932 was appointed as an assistant at the Ivanovo Pedagogical Institute located in Ivanovo, near Moscow. Whilst teaching at Ivanovo, Maltsev made frequent trips to Moscow to discuss his research with Kolmogorov. Maltsev's f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Linear Group
In mathematics, a matrix group is a group ''G'' consisting of invertible matrices over a specified field ''K'', with the operation of matrix multiplication. A linear group is a group that is isomorphic to a matrix group (that is, admitting a faithful, finite-dimensional representation over ''K''). Any finite group is linear, because it can be realized by permutation matrices using Cayley's theorem. Among infinite groups, linear groups form an interesting and tractable class. Examples of groups that are not linear include groups which are "too big" (for example, the group of permutations of an infinite set), or which exhibit some pathological behavior (for example, finitely generated infinite torsion groups). Definition and basic examples A group ''G'' is said to be ''linear'' if there exists a field ''K'', an integer ''d'' and an injective homomorphism from ''G'' to the general linear group GL''d''(''K'') (a faithful linear representation of dimension ''d'' over ''K''): if ne ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Residually Finite
{{unsourced, date=September 2022 In the mathematical field of group theory, a group ''G'' is residually finite or finitely approximable if for every element ''g'' that is not the identity in ''G'' there is a homomorphism ''h'' from ''G'' to a finite group, such that :h(g) \neq 1.\, There are a number of equivalent definitions: *A group is residually finite if for each non-identity element in the group, there is a normal subgroup of finite index not containing that element. *A group is residually finite if and only if the intersection of all its subgroups of finite index is trivial. *A group is residually finite if and only if the intersection of all its normal subgroups of finite index is trivial. *A group is residually finite if and only if it can be embedded inside the direct product of a family of finite groups. Examples Examples of groups that are residually finite are finite groups, free groups, finitely generated nilpotent groups, polycyclic-by-finite groups, f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hopfian Group
In mathematics, a Hopfian group is a group ''G'' for which every epimorphism :''G'' → ''G'' is an isomorphism. Equivalently, a group is Hopfian if and only if it is not isomorphic to any of its proper quotients. A group ''G'' is co-Hopfian if every monomorphism :''G'' → ''G'' is an isomorphism. Equivalently, ''G'' is not isomorphic to any of its proper subgroups. Examples of Hopfian groups * Every finite group, by an elementary counting argument. * More generally, every polycyclic-by-finite group. * Any finitely generated free group. * The group Q of rationals. * Any finitely generated residually finite group. * Any word-hyperbolic group. Examples of non-Hopfian groups * Quasicyclic groups. * The group R of real numbers. * The Baumslag–Solitar group ''B''(2,3). Properties It was shown by that it is an undecidable problem to determine, given a finite presentation of a group, whether the group is Hopfian. Unlike the undecidability of many properties of groups th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Donald Solitar
Donald Solitar (September 5, 1932 in Brooklyn, New York, United States – April 28, 2008 in Toronto, Canada) was an American and Canadian mathematician, known for his work in combinatorial group theory.. Reprinted as and as . The Baumslag–Solitar groups are named after him and Gilbert Baumslag, after their joint 1962 paper on these groups. Life Solitar competed on the mathematics team of Brooklyn Technical High School with his future co-author Abe Karrass, one year ahead of him in school. He graduated from Brooklyn College in 1953 (with the assistance of tutoring from Karrass, who went to New York University) and went to Princeton University for graduate study in mathematics. However, his intended mentor there, Emil Artin, was no longer interested in group theory, so he left with a master's degree and earned his doctorate from New York University instead, in 1958, under the supervision of Wilhelm Magnus. After finishing his studies, he joined the faculty of Adelphi University i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gilbert Baumslag
Gilbert Baumslag (April 30, 1933 – October 20, 2014) was a Distinguished Professor at the City College of New York, with joint appointments in mathematics, computer science, and electrical engineering. He was director of thCenter for Algorithms and Interactive Scientific Software which grew out of the MAGNUS computational group theory project he also headed. Baumslag was also the organizer of the New York Group Theory Seminar. Baumslag graduated from the University of the Witwatersrand in South Africa with a Bachelor of Science, B.Sc. Honours (Masters) and Doctor of Science, D.Sc. He earned his Doctor of Philosophy, Ph.D. from the University of Manchester in 1958; his thesis, written under the direction of Bernhard Neumann, was titled ''Some aspects of groups with unique roots''. His contributions include the Baumslag–Solitar groups and parafree groups. Baumslag was a visiting scholar at the Institute for Advanced Study in 1968–69. In 2012 he became a fellow of the American ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fundamental Group
In the mathematical field of algebraic topology, the fundamental group of a topological space is the group of the equivalence classes under homotopy of the loops contained in the space. It records information about the basic shape, or holes, of the topological space. The fundamental group is the first and simplest homotopy group. The fundamental group is a homotopy invariant—topological spaces that are homotopy equivalent (or the stronger case of homeomorphic) have isomorphic fundamental groups. The fundamental group of a topological space X is denoted by \pi_1(X). Intuition Start with a space (for example, a surface), and some point in it, and all the loops both starting and ending at this point— paths that start at this point, wander around and eventually return to the starting point. Two loops can be combined in an obvious way: travel along the first loop, then along the second. Two loops are considered equivalent if one can be deformed into the other without breakin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Generating Set Of A Group
In abstract algebra, a generating set of a group is a subset of the group set such that every element of the group can be expressed as a combination (under the group operation) of finitely many elements of the subset and their inverses. In other words, if ''S'' is a subset of a group ''G'', then , the ''subgroup generated by S'', is the smallest subgroup of ''G'' containing every element of ''S'', which is equal to the intersection over all subgroups containing the elements of ''S''; equivalently, is the subgroup of all elements of ''G'' that can be expressed as the finite product of elements in ''S'' and their inverses. (Note that inverses are only needed if the group is infinite; in a finite group, the inverse of an element can be expressed as a power of that element.) If ''G'' = , then we say that ''S'' ''generates'' ''G'', and the elements in ''S'' are called ''generators'' or ''group generators''. If ''S'' is the empty set, then is the trivial group , since we consider th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
