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Hall–Petresco Identity
In mathematics, the Hall–Petresco identity (sometimes misspelled Hall–Petrescu identity) is an identity holding in any group. It was introduced by and . It can be proved using the commutator collecting process In group theory, a branch of mathematics, the commutator collecting process is a method for writing an element of a group as a product of generators and their higher commutators arranged in a certain order. The commutator collecting process was int ..., and implies that ''p''-groups of small class are regular p-group, regular. Statement The Hall–Petresco identity states that if ''x'' and ''y'' are elements of a group ''G'' and ''m'' is a positive integer then :x^my^m=(xy)^mc_2^c_3^\cdots c_^c_m where each ''c''''i'' is in the subgroup ''K''''i'' of the descending central series of ''G''. See also * Baker–Campbell–Hausdorff formula * Universal enveloping algebra#Algebra of symbols, Algebra of symbols References

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Commutator Collecting Process
In group theory, a branch of mathematics, the commutator collecting process is a method for writing an element of a group as a product of generators and their higher commutators arranged in a certain order. The commutator collecting process was introduced by Philip Hall in 1934 and articulated by Wilhelm Magnus in 1937. W. Magnus (1937), "Über Beziehungen zwischen höheren Kommutatoren", ''J. Grelle'' 177, 105-115. The process is sometimes called a "collection process". The process can be generalized to define a totally ordered subset of a free non-associative algebra, that is, a free magma; this subset is called the Hall set. Members of the Hall set are binary trees; these can be placed in one-to-one correspondence with words, these being called the Hall words; the Lyndon words are a special case. Hall sets are used to construct a basis for a free Lie algebra, entirely analogously to the commutator collecting process. Hall words also provide a unique factorization of monoids ...
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Regular P-group
In mathematical finite group theory, the concept of regular ''p''-group captures some of the more important properties of abelian ''p''-groups, but is general enough to include most "small" ''p''-groups. Regular ''p''-groups were introduced by . Definition A finite ''p''-group ''G'' is said to be regular if any of the following equivalent , conditions are satisfied: * For every ''a'', ''b'' in ''G'', there is a ''c'' in the derived subgroup ''H''′ of the subgroup ''H'' of ''G'' generated by ''a'' and ''b'', such that ''a''''p'' · ''b''''p'' = (''ab'')''p'' · ''c''''p''. * For every ''a'', ''b'' in ''G'', there are elements ''c''''i'' in the derived subgroup of the subgroup generated by ''a'' and ''b'', such that ''a''''p'' · ''b''''p'' = (''ab'')''p'' · ''c''1''p'' ⋯ ''c''k''p''. * For every ''a'', ''b'' in ''G'' and every positive integer ''n'', there are elements ''c''''i'' in the derived subgroup of the subgroup generated by ''a'' and ''b'' such that ''a''''q'' · ...
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Universal Enveloping Algebra
In mathematics, the universal enveloping algebra of a Lie algebra is the unital associative algebra whose representations correspond precisely to the representations of that Lie algebra. Universal enveloping algebras are used in the representation theory of Lie groups and Lie algebras. For example, Verma modules can be constructed as quotients of the universal enveloping algebra. In addition, the enveloping algebra gives a precise definition for the Casimir operators. Because Casimir operators commute with all elements of a Lie algebra, they can be used to classify representations. The precise definition also allows the importation of Casimir operators into other areas of mathematics, specifically, those that have a differential algebra. They also play a central role in some recent developments in mathematics. In particular, their dual provides a commutative example of the objects studied in non-commutative geometry, the quantum groups. This dual can be shown, by the Gelfand–N ...
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Springer-Verlag
Springer Science+Business Media, commonly known as Springer, is a German multinational publishing company of books, e-books and peer-reviewed journals in science, humanities, technical and medical (STM) publishing. Originally founded in 1842 in Berlin, it expanded internationally in the 1960s, and through mergers in the 1990s and a sale to venture capitalists it fused with Wolters Kluwer and eventually became part of Springer Nature in 2015. Springer has major offices in Berlin, Heidelberg, Dordrecht, and New York City. History Julius Springer founded Springer-Verlag in Berlin in 1842 and his son Ferdinand Springer grew it from a small firm of 4 employees into Germany's then second largest academic publisher with 65 staff in 1872.Chronology
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In 1964, Springer expanded its business internationally, o ...
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