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Wolfgang Krull
Wolfgang Krull (26 August 1899 – 12 April 1971) was a German mathematician who made fundamental contributions to commutative algebra, introducing concepts that are now central to the subject. Krull was born and went to school in Baden-Baden. He attended the Universities of Freiburg, Rostock and finally Göttingen from 1919–1921, where he earned his doctorate under Alfred Loewy. He worked as an instructor and professor at Freiburg, then spent a decade at the University of Erlangen. In 1939, Krull moved to become chair at the University of Bonn, where he remained for the rest of his life. Wolfgang Krull was a member of the Nazi Party. His 35 doctoral students include Wilfried Brauer, Karl-Otto Stöhr and Jürgen Neukirch. See also * Cohen structure theorem * Jacobson ring * Local ring * Prime ideal * Real algebraic geometry * Regular local ring * Valuation ring * Krull dimension In commutative algebra, the Krull dimension of a commutative ring ''R'', named after Wol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prime Ideal
In algebra, a prime ideal is a subset of a ring (mathematics), ring that shares many important properties of a prime number in the ring of Integer#Algebraic properties, integers. The prime ideals for the integers are the sets that contain all the multiple (mathematics), multiples of a given prime number, together with the zero ideal. Primitive ideals are prime, and prime ideals are both primary ideal, primary and semiprime ideal, semiprime. Prime ideals for commutative rings Definition An ideal (ring theory), ideal of a commutative ring is prime if it has the following two properties: * If and are two elements of such that their product is an element of , then is in or is in , * is not the whole ring . This generalizes the following property of prime numbers, known as Euclid's lemma: if is a prime number and if divides a product of two integers, then divides or divides . We can therefore say :A positive integer is a prime number if and only if n\Z is a prime ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Krull's Theorem
In mathematics, and more specifically in ring theory, Krull's theorem, named after Wolfgang Krull, asserts that a nonzero ring has at least one maximal ideal. The theorem was proved in 1929 by Krull, who used transfinite induction. The theorem admits a simple proof using Zorn's lemma, and in fact is equivalent to Zorn's lemma, which in turn is equivalent to the axiom of choice. Variants * For noncommutative rings, the analogues for maximal left ideals and maximal right ideals also hold. * For pseudo-rings, the theorem holds for regular ideals. * An ''apparently'' slightly stronger (but equivalent) result, which can be proved in a similar fashion, is as follows: :::Let ''R'' be a ring, and let ''I'' be a proper ideal of ''R''. Then there is a maximal ideal of ''R'' containing ''I''. :The statement of the original theorem can be obtained by taking ''I'' to be the zero ideal (0). Conversely, applying the original theorem to ''R''/''I'' leads to this result. :To prove the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Krull's Separation Lemma
In abstract algebra, Krull's separation lemma is a lemma in ring theory. It was proved by Wolfgang Krull in 1928. Statement of the lemma Let I be an ideal and let M be a multiplicative system (''i.e.'' M is closed under multiplication) in a ring R, and suppose I \cap M = \varnothing. Then there exists a prime ideal In algebra, a prime ideal is a subset of a ring (mathematics), ring that shares many important properties of a prime number in the ring of Integer#Algebraic properties, integers. The prime ideals for the integers are the sets that contain all th ... P satisfying I \subseteq P and P \cap M = \varnothing. References Theorems in ring theory Lemmas {{algebra-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Krull's Principal Ideal Theorem
In commutative algebra, Krull's principal ideal theorem, named after Wolfgang Krull (1899–1971), gives a bound on the height of a principal ideal in a commutative Noetherian ring. The theorem is sometimes referred to by its German name, ''Krulls Hauptidealsatz'' (from ' ("Principal") + ' + ' ("theorem")). Precisely, if ''R'' is a Noetherian ring and ''I'' is a principal, proper ideal of ''R'', then each minimal prime ideal containing ''I'' has height at most one. This theorem can be generalized to ideals that are not principal, and the result is often called Krull's height theorem. This says that if ''R'' is a Noetherian ring and ''I'' is a proper ideal generated by ''n'' elements of ''R'', then each minimal prime over ''I'' has height at most ''n''. The converse is also true: if a prime ideal has height ''n'', then it is a minimal prime ideal over an ideal generated by ''n'' elements. The principal ideal theorem and the generalization, the height theorem, both follow from ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Krull–Schmidt Theorem
In mathematics, the Krull–Schmidt theorem states that a group subjected to certain finiteness conditions on chains of subgroups, can be uniquely written as a finite direct product of indecomposable subgroups. Definitions We say that a group ''G'' satisfies the ascending chain condition (ACC) on subgroups if every sequence of subgroups of ''G'': :1 = G_0 \le G_1 \le G_2 \le \cdots\, is eventually constant, i.e., there exists ''N'' such that ''G''''N'' = ''G''''N''+1 = ''G''''N''+2 = ... . We say that ''G'' satisfies the ACC on normal subgroups if every such sequence of normal subgroups of ''G'' eventually becomes constant. Likewise, one can define the descending chain condition on (normal) subgroups, by looking at all decreasing sequences of (normal) subgroups: :G = G_0 \ge G_1 \ge G_2 \ge \cdots.\, Clearly, all finite groups satisfy both ACC and DCC on subgroups. The infinite cyclic group \mathbf satisfies ACC but not DCC, since (2) > (2)2 >&n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Krull–Schmidt Category
In category theory, a branch of mathematics, a Krull–Schmidt category is a generalization of categories in which the Krull–Schmidt theorem holds. They arise, for example, in the study of finite-dimensional modules over an algebra. Definition Let ''C'' be an additive category, or more generally an additive -linear category for a commutative ring . We call ''C'' a Krull–Schmidt category provided that every object decomposes into a finite direct sum of objects having local endomorphism rings. Equivalently, ''C'' has split idempotents and the endomorphism ring of every object is semiperfect. Properties One has the analogue of the Krull–Schmidt theorem in Krull–Schmidt categories: An object is called ''indecomposable'' if it is not isomorphic to a direct sum of two nonzero objects. In a Krull–Schmidt category we have that *an object is indecomposable if and only if its endomorphism ring is local. *every object is isomorphic to a finite direct sum of indecompos ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nakayama's Lemma
In mathematics, more specifically abstract algebra and commutative algebra, Nakayama's lemma — also known as the Krull–Azumaya theorem — governs the interaction between the Jacobson radical of a ring (typically a commutative ring) and its finitely generated modules. Informally, the lemma immediately gives a precise sense in which finitely generated modules over a commutative ring behave like vector spaces over a field. It is an important tool in algebraic geometry, because it allows local data on algebraic varieties, in the form of modules over local rings, to be studied pointwise as vector spaces over the residue field of the ring. The lemma is named after the Japanese mathematician Tadashi Nakayama and introduced in its present form in , although it was first discovered in the special case of ideals in a commutative ring by Wolfgang Krull and then in general by Goro Azumaya (1951). In the commutative case, the lemma is a simple consequence of a generalized fo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Krull Topology
In mathematics, a profinite group is a topological group that is in a certain sense assembled from a system of finite groups. The idea of using a profinite group is to provide a "uniform", or "synoptic", view of an entire system of finite groups. Properties of the profinite group are generally speaking uniform properties of the system. For example, the profinite group is finitely generated (as a topological group) if and only if there exists d\in\N such that every group in the system can be generated by d elements. Many theorems about finite groups can be readily generalised to profinite groups; examples are Lagrange's theorem and the Sylow theorems. To construct a profinite group one needs a system of finite groups and group homomorphisms between them. Without loss of generality, these homomorphisms can be assumed to be surjective, in which case the finite groups will appear as quotient groups of the resulting profinite group; in a sense, these quotients approximate the profini ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Krull Ring
In commutative algebra, a Krull ring, or Krull domain, is a commutative ring with a well behaved theory of prime factorization. They were introduced by Wolfgang Krull in 1931. They are a higher-dimensional generalization of Dedekind domains, which are exactly the Krull domains of dimension at most 1. In this article, a ring is commutative and has unity. Formal definition Let A be an integral domain and let P be the set of all prime ideals of A of height one, that is, the set of all prime ideals properly containing no nonzero prime ideal. Then A is a Krull ring if # A_ is a discrete valuation ring for all \mathfrak \in P , # A is the intersection of these discrete valuation rings (considered as subrings of the quotient field of A ), #any nonzero element of A is contained in only a finite number of height 1 prime ideals. It is also possible to characterize Krull rings by mean of valuations only: An integral domain A is a Krull ring if there exists a family \ _ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Krull Dimension
In commutative algebra, the Krull dimension of a commutative ring ''R'', named after Wolfgang Krull, is the supremum of the lengths of all chains of prime ideals. The Krull dimension need not be finite even for a Noetherian ring. More generally the Krull dimension can be defined for modules over possibly non-commutative rings as the deviation of the poset of submodules. The Krull dimension was introduced to provide an algebraic definition of the dimension of an algebraic variety: the dimension of the affine variety defined by an ideal ''I'' in a polynomial ring ''R'' is the Krull dimension of ''R''/''I''. A field ''k'' has Krull dimension 0; more generally, ''k'' 'x''1, ..., ''x''''n''has Krull dimension ''n''. A principal ideal domain that is not a field has Krull dimension 1. A local ring has Krull dimension 0 if and only if every element of its maximal ideal is nilpotent. There are several other ways that have been used to define the dimension of a ring. Most of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |