scholarly journals An Exact Sequence Associated with a Generalized Crossed Product

1973 ◽  
Vol 49 ◽  
pp. 21-51 ◽  
Author(s):  
Yôichi Miyashita
Keyword(s):  
Exact Sequence ◽  
Crossed Product ◽  
Group Homomorphism ◽  
Ring Extension ◽  
Exact Sequences

The purpose of this paper is to generalize the seven terms exact sequence given by Chase, Harrison and Rosenberg [8]. Our work was motivated by Kanzaki [16] and, of course, [8], [9]. The main theorem holds for any generalized crossed product, which is a more general one than that in Kanzaki [16]. In §1, we define a group P(A/B) for any ring extension A/B, and prove some preliminary exact sequences. In §2, we fix a group homomorphism J from a group G to the group of all invertible two-sided B-submodules of A.

Cellular covers of ℵ1-free abelian groups

2015 ◽  
Vol 14 (10) ◽  
pp. 1550139 ◽  
Author(s):  
José L. Rodríguez ◽  
Lutz Strüngmann
Keyword(s):  
Abelian Group ◽  
Exact Sequence ◽  
Free Abelian Group ◽  
Abelian Groups ◽  
Countable Rank ◽  
Free Abelian Groups ◽  
Rank 2 ◽  
Exact Sequences ◽  
Torsion Free ◽  
Cellular Cover

In this paper, we first show that for every natural number n and every countable reduced cotorsion-free group K there is a short exact sequence [Formula: see text] such that the map G → H is a cellular cover over H and the rank of H is exactly n. In particular, the free abelian group of infinite countable rank is the kernel of a cellular exact sequence of co-rank 2 which answers an open problem from Rodríguez–Strüngmann [J. L. Rodríguez and L. Strüngmann, Mediterr. J. Math.6 (2010) 139–150]. Moreover, we give a new method to construct cellular exact sequences with prescribed torsion free kernels and cokernels. In particular we apply this method to the class of ℵ1-free abelian groups in order to complement results from the cited work and Göbel–Rodríguez–Strüngmann [R. Göbel, J. L. Rodríguez and L. Strüngmann, Fund. Math.217 (2012) 211–231].

scholarly journals Non-abelian exterior products of groups and exact sequences in the homology of groups

1987 ◽  
Vol 29 (1) ◽  
pp. 13-19 ◽  
Author(s):  
G. J. Ellis
Keyword(s):  
Exact Sequence ◽  
Short Exact Sequence ◽  
Type Theorem ◽  
Exterior Product ◽  
Products Of Groups ◽  
Hopf Formula ◽  
Definition Of ◽  
Image Position ◽  
Exact Sequences

Various authors have obtained an eight term exact sequence in homologyfrom a short exact sequence of groups,the term V varying from author to author (see [7] and [2]; see also [5] for the simpler case where N is central in G, and [6] for the case where N is central and N ⊂ [G, G]). The most satisfying version of the sequence is obtained by Brown and Loday [2] (full details of [2] are in [3]) as a corollary to their van Kampen type theorem for squares of spaces: they give the term V as the kernel of a map G ∧ N → N from a “non-abelian exterior product” of G and N to the group N (the definition of G ∧ N, first published in [2], is recalled below). The two short exact sequencesandwhere F is free, together with the fact that H2(F) = 0 and H3(F) = 0, imply isomorphisms..The isomorphism (2) is essentially the description of H2(G) proved algebraically in [11]. As noted in [2], the isomorphism (3) is the analogue for H3(G) of the Hopf formula for H2(G).

scholarly journals SPECTRAL INVARIANCE OF DENSE SUBALGEBRAS OF OPERATOR ALGEBRAS

1993 ◽  
Vol 04 (02) ◽  
pp. 289-317 ◽  
Author(s):  
LARRY B. SCHWEITZER
Keyword(s):  
Polynomial Growth ◽  
Operator Algebras ◽  
Crossed Product ◽  
Discrete Groups ◽  
Spectral Invariance ◽  
C Algebra ◽  
C Algebras ◽  
Schwartz Functions ◽  
Exact Sequences ◽  
Spectral Invariant

We define the notion of strong spectral invariance for a dense Fréchet subalgebra A of a Banach algebra B. We show that if A is strongly spectral invariant in a C*-algebra B, and G is a compactly generated polynomial growth Type R Lie group, not necessarily connected, then the smooth crossed product G ⋊ A is spectral invariant in the C*-crossed product G ⋊ B. Examples of such groups are given by finitely generated polynomial growth discrete groups, compact or connected nilpotent Lie groups, the group of Euclidean motions on the plane, the Mautner group, or any closed subgroup of one of these. Our theorem gives the spectral invariance of G ⋊ A if A is the set of C∞-vectors for the action of G on B, or if B = C0 (M), and A is a set of G-differentiable Schwartz functions [Formula: see text] on M. This gives many examples of spectral invariant dense subalgebras for the C*-algebras associated with dynamical systems. We also obtain relevant results about exact sequences, subalgebras, tensoring by smooth compact operators, and strong spectral invariance in L1 (G, B).

Neat-phantom and clean-cophantom morphisms

2020 ◽  
pp. 2150172
Author(s):  
Lixin Mao
Keyword(s):  
Exact Sequence ◽  
Projective Resolution ◽  
Injective Envelope ◽  
Finitely Generated ◽  
The Relationship ◽  
Exact Sequences

Let [Formula: see text] be the class of all left [Formula: see text]-modules [Formula: see text] which has a projective resolution by finitely generated projectives. An exact sequence [Formula: see text] of right [Formula: see text]-modules is called neat if the sequence [Formula: see text] is exact for any [Formula: see text]. An exact sequence [Formula: see text] of left [Formula: see text]-modules is called clean if the sequence [Formula: see text] is exact for any [Formula: see text]. We prove that every [Formula: see text]-module has a clean-projective precover and a neat-injective envelope. A morphism [Formula: see text] of right [Formula: see text]-modules is called a neat-phantom morphism if [Formula: see text] for any [Formula: see text]. A morphism [Formula: see text] of left [Formula: see text]-modules is said to be a clean-cophantom morphism if [Formula: see text] for any [Formula: see text]. We establish the relationship between neat-phantom (respectively, clean-cophantom) morphisms and neat (respectively, clean) exact sequences. Also, we prove that every [Formula: see text]-module has a neat-phantom cover with kernel neat-injective and a clean-cophantom preenvelope with cokernel clean-projective.

scholarly journals The category of long exact sequences and the homotopy exact sequence of modules

2003 ◽  
Vol 2003 (22) ◽  
pp. 1383-1395 ◽  
Author(s):  
C. Joanna Su
Keyword(s):  
Exact Sequence ◽  
Full Subcategory ◽  
Homotopy Theory ◽  
Alternative Proof ◽  
Abelian Categories ◽  
The Absolute ◽  
Relative Category ◽  
Exact Sequences

The relative homotopy theory of modules, including the (module) homotopy exact sequence, was developed by Peter Hilton (1965). Our thrust is to produce an alternative proof of the existence of the injective homotopy exact sequence with no reference to elements of sets, so that one can define the necessary homotopy concepts in arbitrary abelian categories with enough injectives and projectives, and obtain, automatically, the projective relative homotopy theory as the dual. Furthermore, we pursue the relative (module) homotopy theory analogously to the absolute (module) homotopy theory. For these purposes, we embed the relative category into the category of long exact sequences, as a full subcategory, in our search for suitable notions of monomorphisms and injectives in the relative category.

scholarly journals QUIVERS, LONG EXACT SEQUENCES AND HORN TYPE INEQUALITIES II

2009 ◽  
Vol 51 (2) ◽  
pp. 201-217
Author(s):  
CALIN CHINDRIS
Keyword(s):  
Exact Sequence ◽  
Spectral Problem ◽  
Linear Algebra ◽  
Special Issue ◽  
Hermitian Matrices ◽  
Exact Sequences ◽  
Combinatorial Methods

AbstractWe study the set of all m-tuples (λ(1), . . ., λ(m)) of possible types of finite abelian p-groups Mλ(1), . . ., Mλ(m) for which there exists a long exact sequence Mλ(1) → ⋅⋅⋅ → Mλ(m). When m=3, we recover W. Fulton's (Eigenvalues of majorized Hermitian matrices and Littlewood-Richardson coefficients (Special Issue: Workshop on Geometric and combinatorial Methods in the Hermitian Sum Spectral Problem), Linear Algebra Appl. 319(1–3) (2000), 23–36) results on the possible eigenvalues of majorized Hermitian matrices.

Localization and class groups of module categories with exactness defects

1993 ◽  
Vol 113 (2) ◽  
pp. 233-251 ◽  
Author(s):  
D. Holland ◽  
S. M. J. Wilson
Keyword(s):  
Exact Sequence ◽  
Class Group ◽  
Grothendieck Group ◽  
Module Category ◽  
Class Groups ◽  
Definition Of ◽  
Free Modules ◽  
Exact Sequences ◽  
Torsion Free

AbstractWe present a new way of forming a grothendieck group with respect to exact sequences. A ‘defect’ is attached to each non-split sequence and the relation that would normally be derived from a collection of exact sequences is only effective if the (signed) sum of the corresponding defects is zero. The theory of the localization exact sequence and, in particular, of the relative group in this sequence is developed. The (‘locally free’) class group of a module category with exactness defect is defined and an idèlic formula for this is given. The role of torsion and of torsion-free modules is investigated. One aim of the work is to enhance the locally trivial, ‘class group’, invariants obtainable for a module while keeping to a minimum the local obstructions to the definition of such invariants.

THE BRAID GROUP $B_{n,m}(\mathbb{S}^{2})$ AND A GENERALISATION OF THE FADELL–NEUWIRTH SHORT EXACT SEQUENCE

2005 ◽  
Vol 14 (03) ◽  
pp. 375-403 ◽  
Author(s):  
DACIBERG LIMA GONÇALVES ◽  
JOHN GUASCHI
Keyword(s):  
Exact Sequence ◽  
Symmetric Group ◽  
Cross Section ◽  
Short Exact Sequence ◽  
Braid Group ◽  
Configuration Spaces ◽  
Group Homomorphism

Let m,n ∈ ℕ. We define [Formula: see text] to be the set of (n+m)-braids of the sphere whose associated permutation lies in the subgroup Sn × Sm of the symmetric group Sn+m on n+m letters. In a previous paper [13], we showed that if n ≥ 3, then there exists the following generalisation of the Fadell–Neuwirth short exact sequence: [Formula: see text] where [Formula: see text] is the group homomorphism (defined for all n ∈ ℕ) given geometrically by forgetting the last m strings. In this paper we study the splitting of this short exact sequence, as well as the existence of a cross-section for the fibration [Formula: see text] of the quotients of the corresponding configuration spaces. Our main results are as follows: if n = 1 (respectively, n = 2) then the homomorphism p* and the fibration p admit (respectively, do not admit) a section. If n = 3, then p* and p admit a section if and only if m ≡ 0,2 (mod 3). If n ≥ 4, we show that if p* and p admit a section then m ≡ ε1(n - 1)(n - 2) - ε2n(n - 2) (mod n(n - 1)(n - 2)), where ε1,ε2 ∈ {0,1}. Finally, we show that [Formula: see text] is generated by two of its torsion elements.

Exact Sequences for the Kasparov Groups of Graded Algebras

1985 ◽  
Vol 37 (2) ◽  
pp. 193-216 ◽  
Author(s):  
George Skandalis
Keyword(s):  
Exact Sequence ◽  
Free Groups ◽  
Crossed Products ◽  
Graded Algebras ◽  
Completely Positive ◽  
Exact Sequences

In [11] G. G. Kasparov defined the “operator K-functor” KK(A, B) associated with the graded C*-algebras A and B. If the algebras A and B are trivially graded and A is nuclear he proves six term exact sequence theorems. He asks whether this extends to the graded case.Here we prove such “six-term exact sequence” results in the graded case. Our proof does not use nuclearity of the algebra A. This condition is replaced by a completely positive lifting condition (Theorem 1.1).Using our result we may extend the results by M. Pimsner and D. Voiculescu on the K groups of crossed products by free groups to KK groups [15]. We give however a different way of computing these groups using the equivariant KK-theory developed by G. G. Kasparov in [12]. This method also allows us to compute the KK groups of crossed products by PSL2(Z).

scholarly journals Dehn twist exact sequences through Lagrangian cobordism

2018 ◽  
Vol 154 (12) ◽  
pp. 2485-2533 ◽  
Author(s):  
Cheuk Yu Mak ◽  
Weiwei Wu
Keyword(s):  
Fixed Point ◽  
Exact Sequence ◽  
Symplectic Geometry ◽  
Dehn Twist ◽  
Partial Answer ◽  
Lagrangian Cobordism ◽  
Exact Sequences

This paper introduces a new Lagrangian surgery construction that generalizes Lalonde–Sikorav and Polterovich’s well-known construction, and combines this with Biran and Cornea’s Lagrangian cobordism formalism. With these techniques, we build a framework which both recovers several known long exact sequences (Seidel’s exact sequence, including the fixed point version and Wehrheim and Woodward’s family version) in symplectic geometry in a uniform way, and yields a partial answer to a long-term open conjecture due to Huybrechts and Thomas; this also involved a new observation which relates projective twists with surgeries.

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