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In the mathematical  [[surgery theory]] the '''surgery exact sequence''' is the main technical tool to calculate the [[surgery structure set]] of a compact [[manifold]] in dimension <math>>4</math>. The [[surgery structure set]] <math>\mathcal{S} (X)</math> of a compact <math>n</math>-dimensional manifold <math>X</math> is a pointed set which classifies <math>n</math>-dimensional manifolds within the homotopy type of <math>X</math>.


The basic idea is that in order to calculate <math>\mathcal{S} (X)</math> it is enough to understand the other terms in the sequence, which are usually easier to determine. These are on one hand the [[normal invariants]] which form [[Cohomology#Cohomology theories|generalized cohomology groups]], and hence one can use standard tools of algebraic topology to calculate them at least in principle. On the other hand there are the [[L-theory|L-groups]] which are defined algebraically in terms of [[quadratic forms]] or in terms of chain complexes with quadratic structure. A great deal is known about these groups. Another part of the sequence are the [[surgery obstruction]] maps from normal invariants to the L-groups. For these maps there are certain [[characteristic classes]] formulas, which enable to calculate them in some cases. Knowledge of these three components, that means: the normal maps, the L-groups and the surgery obstruction maps is enough to determine the structure set (at least up to extension problems).


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In practice one has to proceed case by case, for each manifold <math>\mathcal{} X</math> it is a unique task to determine the surgery exact sequence, see some examples below. Also note that there are versions of the surgery exact sequence depending on the category of manifolds we work with: smooth (DIFF), PL, or topological manifolds and whether we take Whitehead torsion into account or not (decorations <math>s</math> or <math>h</math>).
 
The original 1962 work of [[William Browder (mathematician)|Browder]] and [[Sergei Novikov (mathematician)|Novikov]] on the existence and uniqueness of manifolds within a [[simply-connected]] homotopy type was reformulated by [[Dennis Sullivan|Sullivan]] in 1966 as a '''surgery exact sequence'''.
In 1970 [[C.T.C. Wall|Wall]] developed [[non-simply-connected]] surgery theory and the surgery exact sequence for manifolds with arbitrary fundamental group.
 
==Definition==
 
The surgery exact sequence is defined as
 
: <math>
\cdots \to \mathcal{N}_\partial (X \times I) \to L_{n+1} (\pi_1 (X)) \to \mathcal{S}(X) \to \mathcal{N} (X) \to L_n (\pi_1 (X))
</math>
 
where:
 
the entries <math>\mathcal{N}_\partial (X \times I)</math> and <math>\mathcal{N} (X)</math> are the abelian groups of [[normal invariants]],
 
the entries <math>\mathcal{} L_{n+1} (\pi_1 (X)) </math> and <math>\mathcal{} L_{n} (\pi_1 (X)) </math> are the [[L-theory|L-groups]] associated to the group ring <math>\mathbb{Z}[\pi_1 (X)]</math>,
 
the maps <math>\theta \colon \mathcal{N}_\partial (X \times I) \to L_{n+1} (\pi_1 (X))</math> and <math>\theta \colon \mathcal{N} (X) \to L_n (\pi_1 (X))</math> are the [[surgery obstruction]] maps,
 
the arrows <math>\partial \colon L_{n+1} (\pi_1 (X)) \to \mathcal{S}(X)</math> and <math>\eta \colon \mathcal{S}(X) \to \mathcal{N} (X)</math> will be explained below.
 
==Versions==
There are various versions of the surgery exact sequence. One can work in either of the three categories of manifolds: differentiable (smooth), PL, topological. Another possibility is to work with the decorations <math>s</math> or <math>h</math>.
 
==The entries==
 
===Normal invariants===
{{main|Normal invariants}}
 
A degree one normal map <math>(f,b) \colon M \to X</math> consists of the following data: an <math>n</math>-dimensional oriented closed manifold <math>M</math>, a map <math>f</math> which is of degree one (that means <math>f_* ([M]) = [X]</math>, and a bundle map <math>b \colon TM \oplus \varepsilon^k \to \xi</math> from the stable tangent bundle of <math>M</math> to some bundle <math>\xi</math> over <math>X</math>. Two such maps are equivalent if there exists a normal bordism between them (that means a bordism of the sources covered by suitable bundle data). The equivalence classes of degree one normal maps are called '''normal invariants'''.
 
When defined like this the normal invariants <math>\mathcal{N} (X)</math> are just a pointed set, with the base point given by <math>(id,id)</math>. However the [[Pontrjagin-Thom construction#Framed cobordism|Pontrjagin-Thom]] construction gives <math>\mathcal{N} (X)</math> a structure of an abelian group. In fact we have a non-natural bijection
 
: <math>\mathcal{N} (X) \cong [X,G/O]</math>
 
where <math>G/O</math> denotes the homotopy fiber of the map <math>J \colon BO \to BG</math>, which is an infinite loop space and hence maps into it define a generalized cohomology theory. There are corresponding identifications of the normal invariants with <math>[X,G/PL]</math> when working with PL-manifolds and with <math>[X,G/TOP]</math> when working with topological manifolds.
 
===L-groups===
{{main|L-theory}}
 
The <math>L</math>-groups are defined algebraically in terms of [[quadratic forms]] or in terms of chain complexes with quadratic structure. See the main article for more details. Here only the properties of the L-groups described below will be important.
 
===Surgery obstruction maps===
{{main|Surgery obstruction}}
 
The map <math>\theta \colon \mathcal{N} (X) \to L_n (\pi_1 (X))</math> is in the first instance a set-theoretic map (that means not necessarily a homomorphism) with the following property (when <math>n \geq 5</math>:
 
A degree one normal map <math>(f,b) \colon M \to X</math> is normally cobordant to a homotopy equivalence if and only if the image <math>\theta (f,b)=0</math> in <math>L_n (\mathbb{Z} [\pi_1 (X)])</math>.
 
===The normal invariants arrow <math>\eta \colon \mathcal{S}(X) \to \mathcal{N} (X)</math>===
 
Any homotopy equivalence <math>f \colon M \to X</math> defines a degree one normal map.
 
===The surgery obstruction arrow <math>\partial \colon L_{n+1} (\pi_1 (X)) \to \mathcal{S}(X)</math>===
 
This arrow describes in fact an action of the group <math>L_{n+1} (\pi_1 (X))</math> on the set <math>\mathcal{S}(X)</math> rather than just a map. The definition is based on the realization theorem for the elements of the <math>L</math>-groups which reads as follows:
 
Let <math>M</math> be an <math>n</math>-dimensional manifold with <math>\pi_1 (M) \cong \pi_1 (X)</math> and let <math>x \in L_{n+1} (\pi_1 (X))</math>. Then there exists a degree one normal map of manifolds with boundary
 
: <math>(F,B) \colon (W,M,M') \to (M \times I, M \times 0, M \times 1)</math>
 
with the following properties:
 
1. <math>\theta (F,B) = x \in L_{n+1} (\pi_1 (X))</math>
 
2. <math>F_0 \colon M \to M \times 0</math> is a diffeomorphism
 
3. <math>F_1 \colon M' \to M \times 1</math> is a homotopy equivalence of closed manifolds
 
Let <math>f \colon M \to X</math> represent an element in <math>\mathcal{S} (X)</math> and let <math>x \in L_{n+1} (\pi_1 (X))</math>. Then <math>\partial (f,x)</math> is defined as <math>f \circ F_1 \colon M' \to X</math>.
 
==The exactness==
 
Recall that the surgery structure set is only a pointed set and that the surgery obstruction map <math>\theta</math> might not be a homomorphism. Hence it is necessary to explain what is meant when talking about the "exact sequence". So the surgery exact sequence is an exact sequence in the following sense:
 
For a normal invariant <math>z \in \mathcal{N} (X)</math> we have <math>z \in  \mathrm{Im} (\eta)</math> if and only if <math>\theta (z) = 0</math>. For two manifold structures <math>x_1, x_2 \in \mathcal{S} (X)</math> we have <math>\eta (x_1) = \eta(x_2)</math> if and only if there exists <math>u \in L_{n+1} (\pi_1 (X))</math> such that <math>\partial (u,x_1) = x_2</math>. For an element <math>u \in L_{n+1} (\pi_1 (X))</math> we have <math>\partial (u,\mathrm{id}) = \mathrm{id}</math> if and only if <math>u \in \mathrm{Im} (\theta)</math>.
 
==Versions revisited==
 
In the topological category the surgery obstruction map can be made into a homomorphism. This is achieved by putting an alternative abelian group structure on the normal invariants as described [[Normal invariants|here]]. Moreover, the surgery exact sequence can be identified with the algebraic surgery exact sequence of Ranicki which is an exact sequence of abelian groups by definition. This gives the structure set <math>\mathcal{S} (X)</math> the structure of an abelian group. Note, however, that there is to this date no satisfactory geometric description of this abelian group structure.
 
==Classification of manifolds==
The answer to the organizing questions of the [[surgery theory]] can be formulated in terms of the surgery exact sequence. In both cases the answer is given in the form of a two-stage obstruction theory.
 
The existence question. Let <math>X</math> be a finite Poincaré complex. It is homotopy equivalent to a manifold if and only if the following two conditions are satisfied. Firstly, <math>X</math> must have a vector bundle reduction of its Spivak normal fibration. This condition can be also formulated as saying that the set of normal invariants <math>\mathcal{N} (X)</math> is non-empty. Secondly, there must be a normal invariant <math>x \in \mathcal{N} (X)</math> such that <math>\theta (x) = 0</math>. Equivalently, the surgery obstruction map <math>\theta  \colon \mathcal{N} (X) \rightarrow L_{n} (\pi_1 (X))</math> hits <math>0 \in L_{n} (\pi_1 (X))</math>.
 
The uniqueness question. Let <math>f \colon M \to X</math> and <math>f' \colon M' \to X</math> represent two elements in the [[surgery structure set]] <math>\mathcal{S} (X)</math>. The question whether they represent the same element can be answered in two stages as follows. First there must be a normal cobordism between the degree one normal maps induced by <math>\mathcal{} f</math> and <math>\mathcal{} f'</math>, this means <math>\mathcal{} \eta (f) = \eta (f')</math> in <math>\mathcal{N} (X)</math>. Denote the normal cobordism <math>(F,B) \colon (W,M,M') \to (X \times I, X \times 0, X \times 1)</math>. If the surgery obstruction <math>\mathcal{} \theta (F,B)</math> in <math>\mathcal{} L_{n+1} (\pi_1 (X))</math> to make this normal cobordism to an [[h-cobordism]] (or [[s-cobordism]]) relative to the boundary vanishes then <math>\mathcal{} f</math> and <math>\mathcal{} f'</math> in fact represent the same element in the [[surgery structure set]].
 
==Examples==
 
===1. [[Homotopy sphere]]s===
 
This is an example in the smooth category, <math>n \geq 5</math>.
 
The idea of the surgery exact sequence is implicitly present already in the original article of Kervaire and Milnor on the groups of homotopy spheres. In the present terminology we have
 
: <math>\mathcal{S}^{DIFF} (S^n) = \Theta^n</math>
 
<math>\mathcal{N}^{DIFF} (S^n) = \Omega^{alm}_n</math> the cobordism group of almost framed <math>n</math> manifolds, <math>\mathcal{N}^{DIFF}_\partial (S^n \times I) = \Omega^{alm}_{n+1}</math>
 
<math>L_n (1) =\mathbb{Z}, 0, \mathbb{Z}_2, 0</math> where <math>n \equiv 0,1,2,3</math> mod <math>4</math> (recall the <math>4</math>-periodicity of the [[L-theory|L-groups]])
 
The surgery exact sequence in this case is an exact sequence of abelian groups. In addition to the above identifications we have
 
<math>bP^{n+1} = \mathrm{ker} (\eta \colon \mathcal{S}^{DIFF} (S^n) \to \mathcal{N}^{DIFF} (S^n)) = \mathrm{coker} (\theta \colon \mathcal{N}^{DIFF}_\partial (S^n \times I) \to L_{n+1} (1))</math>
 
Because the odd-dimensional L-groups are trivial one obtains these exact sequences:
 
: <math>0 \to \Theta^{4i} \to \Omega^{alm}_{4i} \to \mathbb{Z} \to bP^{4i} \to 0</math>
 
: <math>0 \to \Theta^{4i-2} \to \Omega^{alm}_{4i-2} \to \mathbb{Z}/2 \to bP^{4i-2} \to 0</math>
 
: <math>0 \to bP^{2j} \to \Theta^{2j-1} \to \Omega^{alm}_{2j-1} \to 0</math>
 
The results of Kervaire and Milnor are obtained by studying the middle map in the first two sequences and by relating the groups <math>\Omega_i^{alm}</math> to stable homotopy theory.
 
===2. Topological spheres===
 
The [[generalized Poincaré conjecture]] in dimension <math>n</math> can be phrased as saying that <math>\mathcal{S}^{TOP} (S^n) = 0</math>. It has been proved for any <math>n</math> by the work of Smale, Freedman and Perelman. From the surgery exact sequence for <math>S^n</math> for <math>n \geq 5</math> in the topological category we see that
 
: <math>\theta \colon \mathcal{N}^{TOP} (S^n) \to L_n (1)</math>
 
is an isomorphism. (In fact this can be extended to <math>n \geq 1</math> by some ad-hoc methods.)
 
===3. Complex [[projective space]]s in the topological category===
 
The complex projective space <math>\mathbb{C} P^n</math> is a <math>(2n)</math>-dimensional topological manifold with <math>\pi_1 (\mathbb{C} P^n)=1</math>. In addition it is known that in the case <math>\pi_1 (X) =1</math> in the topological category the surgery obstruction map <math>\theta</math> is always surjective. Hence we have
 
: <math>0 \to \mathcal{S}^{TOP} (\mathbb{C} P^n) \to \mathcal{N}^{TOP} (\mathbb{C} P^n) \to L_{2n}(1) \to 0</math>
 
From the work of Sullivan one can calculate
 
: <math>\mathcal{N} (\mathbb{C} P^n) \cong \oplus_{i=1}^{\lfloor n/2 \rfloor} \mathbb{Z} \oplus \oplus_{i=1}^{\lfloor (n+1)/2 \rfloor} \mathbb{Z}_2</math> and hence <math>\mathcal{S} (\mathbb{C} P^n) \cong \oplus_{i=1}^{\lfloor (n-1)/2 \rfloor} \mathbb{Z} \oplus \oplus_{i=1}^{\lfloor n/2 \rfloor} \mathbb{Z}_2</math>
 
===4. [[Aspherical space|Aspherical]] manifolds in the topological category===
 
An aspherical <math>n</math>-dimensional manifold <math>X</math> is an <math>n</math>-manifold such that <math>\pi_i (X) = 0</math> for <math>i \geq 2</math>. Hence the only non-trivial homotopy group is <math>\pi_1 (X)</math>
 
One way to state the [[Borel conjecture]] is to say that for such <math>X</math> we have that the [[Whitehead group]] <math>Wh (\pi_1 (X))</math> is trivial and that
 
: <math>\mathcal{S} (X) = 0</math>
 
This conjecture was proven in many special cases - for example when <math>\pi_1 (X)</math> is <math>\mathbb{Z}^n</math>, when it is the fundamental group of a negatively curved manifold or when it is a word-hyperbolic group or a CAT(0)-group.
 
The statement is equivalent to showing that the surgery obstruction map to the right of the surgery structure set is injective and the surgery obstruction map to the left of the surgery structure set is surjective. Most of the proofs of the above mentioned results are done by studying these maps or by studying the [[assembly map]]s with which they can be identified. See more details in [[Borel conjecture]], [[Farrell-Jones Conjecture]].
 
==References==
*{{Citation | last1=Browder | first1=William | title=Surgery on simply-connected manifolds | publisher=[[Springer-Verlag]] | location=Berlin, New York | id={{MathSciNet | id = 0358813}} | year=1972}}
*{{Citation | last1=Lück | first1=Wolfgang | title=A basic introduction to surgery theory | url=http://131.220.77.52/lueck/data/ictp.pdf  | publisher= ICTP Lecture Notes Series 9, Band 1, of the school "High-dimensional manifold theory" in Trieste, May/June 2001, Abdus Salam International Centre for Theoretical Physics, Trieste 1-224 | year=2002}}
*{{Citation | last1=Ranicki | first1=Andrew | title =  Algebraic L-theory and topological manifolds | publisher=[[Cambridge University Press]] | series = Cambridge Tracts in Mathematics | url = http://www.maths.ed.ac.uk/~aar/books/topman.pdf  | year = 1992| volume=102 }}
*{{Citation | last1=Ranicki | first1=Andrew | title=Algebraic and Geometric Surgery | url=http://www.maths.ed.ac.uk/~aar/books/surgery.pdf  | publisher=Oxford Mathematical Monographs, Clarendon Press | isbn=978-0-19-850924-0 | id={{MathSciNet | id = 2061749}} | year=2002}}
*{{Citation | last1=Wall | first1=C. T. C. | title=Surgery on compact manifolds | publisher=[[American Mathematical Society]] | location=Providence, R.I. | edition=2nd | series=Mathematical Surveys and Monographs | isbn=978-0-8218-0942-6 | id={{MathSciNet | id = 1687388}} | year=1999 | volume=69}}
 
[[Category:Surgery theory]]

Revision as of 13:29, 13 October 2013

In the mathematical surgery theory the surgery exact sequence is the main technical tool to calculate the surgery structure set of a compact manifold in dimension >4. The surgery structure set 𝒮(X) of a compact n-dimensional manifold X is a pointed set which classifies n-dimensional manifolds within the homotopy type of X.

The basic idea is that in order to calculate 𝒮(X) it is enough to understand the other terms in the sequence, which are usually easier to determine. These are on one hand the normal invariants which form generalized cohomology groups, and hence one can use standard tools of algebraic topology to calculate them at least in principle. On the other hand there are the L-groups which are defined algebraically in terms of quadratic forms or in terms of chain complexes with quadratic structure. A great deal is known about these groups. Another part of the sequence are the surgery obstruction maps from normal invariants to the L-groups. For these maps there are certain characteristic classes formulas, which enable to calculate them in some cases. Knowledge of these three components, that means: the normal maps, the L-groups and the surgery obstruction maps is enough to determine the structure set (at least up to extension problems).

In practice one has to proceed case by case, for each manifold X it is a unique task to determine the surgery exact sequence, see some examples below. Also note that there are versions of the surgery exact sequence depending on the category of manifolds we work with: smooth (DIFF), PL, or topological manifolds and whether we take Whitehead torsion into account or not (decorations s or h).

The original 1962 work of Browder and Novikov on the existence and uniqueness of manifolds within a simply-connected homotopy type was reformulated by Sullivan in 1966 as a surgery exact sequence. In 1970 Wall developed non-simply-connected surgery theory and the surgery exact sequence for manifolds with arbitrary fundamental group.

Definition

The surgery exact sequence is defined as

𝒩(X×I)Ln+1(π1(X))𝒮(X)𝒩(X)Ln(π1(X))

where:

the entries 𝒩(X×I) and 𝒩(X) are the abelian groups of normal invariants,

the entries Ln+1(π1(X)) and Ln(π1(X)) are the L-groups associated to the group ring [π1(X)],

the maps θ:𝒩(X×I)Ln+1(π1(X)) and θ:𝒩(X)Ln(π1(X)) are the surgery obstruction maps,

the arrows :Ln+1(π1(X))𝒮(X) and η:𝒮(X)𝒩(X) will be explained below.

Versions

There are various versions of the surgery exact sequence. One can work in either of the three categories of manifolds: differentiable (smooth), PL, topological. Another possibility is to work with the decorations s or h.

The entries

Normal invariants

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A degree one normal map (f,b):MX consists of the following data: an n-dimensional oriented closed manifold M, a map f which is of degree one (that means f*([M])=[X], and a bundle map b:TMεkξ from the stable tangent bundle of M to some bundle ξ over X. Two such maps are equivalent if there exists a normal bordism between them (that means a bordism of the sources covered by suitable bundle data). The equivalence classes of degree one normal maps are called normal invariants.

When defined like this the normal invariants 𝒩(X) are just a pointed set, with the base point given by (id,id). However the Pontrjagin-Thom construction gives 𝒩(X) a structure of an abelian group. In fact we have a non-natural bijection

𝒩(X)[X,G/O]

where G/O denotes the homotopy fiber of the map J:BOBG, which is an infinite loop space and hence maps into it define a generalized cohomology theory. There are corresponding identifications of the normal invariants with [X,G/PL] when working with PL-manifolds and with [X,G/TOP] when working with topological manifolds.

L-groups

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The L-groups are defined algebraically in terms of quadratic forms or in terms of chain complexes with quadratic structure. See the main article for more details. Here only the properties of the L-groups described below will be important.

Surgery obstruction maps

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The map θ:𝒩(X)Ln(π1(X)) is in the first instance a set-theoretic map (that means not necessarily a homomorphism) with the following property (when n5:

A degree one normal map (f,b):MX is normally cobordant to a homotopy equivalence if and only if the image θ(f,b)=0 in Ln([π1(X)]).

The normal invariants arrow η:𝒮(X)𝒩(X)

Any homotopy equivalence f:MX defines a degree one normal map.

The surgery obstruction arrow :Ln+1(π1(X))𝒮(X)

This arrow describes in fact an action of the group Ln+1(π1(X)) on the set 𝒮(X) rather than just a map. The definition is based on the realization theorem for the elements of the L-groups which reads as follows:

Let M be an n-dimensional manifold with π1(M)π1(X) and let xLn+1(π1(X)). Then there exists a degree one normal map of manifolds with boundary

(F,B):(W,M,M)(M×I,M×0,M×1)

with the following properties:

1. θ(F,B)=xLn+1(π1(X))

2. F0:MM×0 is a diffeomorphism

3. F1:MM×1 is a homotopy equivalence of closed manifolds

Let f:MX represent an element in 𝒮(X) and let xLn+1(π1(X)). Then (f,x) is defined as fF1:MX.

The exactness

Recall that the surgery structure set is only a pointed set and that the surgery obstruction map θ might not be a homomorphism. Hence it is necessary to explain what is meant when talking about the "exact sequence". So the surgery exact sequence is an exact sequence in the following sense:

For a normal invariant z𝒩(X) we have zIm(η) if and only if θ(z)=0. For two manifold structures x1,x2𝒮(X) we have η(x1)=η(x2) if and only if there exists uLn+1(π1(X)) such that (u,x1)=x2. For an element uLn+1(π1(X)) we have (u,id)=id if and only if uIm(θ).

Versions revisited

In the topological category the surgery obstruction map can be made into a homomorphism. This is achieved by putting an alternative abelian group structure on the normal invariants as described here. Moreover, the surgery exact sequence can be identified with the algebraic surgery exact sequence of Ranicki which is an exact sequence of abelian groups by definition. This gives the structure set 𝒮(X) the structure of an abelian group. Note, however, that there is to this date no satisfactory geometric description of this abelian group structure.

Classification of manifolds

The answer to the organizing questions of the surgery theory can be formulated in terms of the surgery exact sequence. In both cases the answer is given in the form of a two-stage obstruction theory.

The existence question. Let X be a finite Poincaré complex. It is homotopy equivalent to a manifold if and only if the following two conditions are satisfied. Firstly, X must have a vector bundle reduction of its Spivak normal fibration. This condition can be also formulated as saying that the set of normal invariants 𝒩(X) is non-empty. Secondly, there must be a normal invariant x𝒩(X) such that θ(x)=0. Equivalently, the surgery obstruction map θ:𝒩(X)Ln(π1(X)) hits 0Ln(π1(X)).

The uniqueness question. Let f:MX and f:MX represent two elements in the surgery structure set 𝒮(X). The question whether they represent the same element can be answered in two stages as follows. First there must be a normal cobordism between the degree one normal maps induced by f and f, this means η(f)=η(f) in 𝒩(X). Denote the normal cobordism (F,B):(W,M,M)(X×I,X×0,X×1). If the surgery obstruction θ(F,B) in Ln+1(π1(X)) to make this normal cobordism to an h-cobordism (or s-cobordism) relative to the boundary vanishes then f and f in fact represent the same element in the surgery structure set.

Examples

1. Homotopy spheres

This is an example in the smooth category, n5.

The idea of the surgery exact sequence is implicitly present already in the original article of Kervaire and Milnor on the groups of homotopy spheres. In the present terminology we have

𝒮DIFF(Sn)=Θn

𝒩DIFF(Sn)=Ωnalm the cobordism group of almost framed n manifolds, 𝒩DIFF(Sn×I)=Ωn+1alm

Ln(1)=,0,2,0 where n0,1,2,3 mod 4 (recall the 4-periodicity of the L-groups)

The surgery exact sequence in this case is an exact sequence of abelian groups. In addition to the above identifications we have

bPn+1=ker(η:𝒮DIFF(Sn)𝒩DIFF(Sn))=coker(θ:𝒩DIFF(Sn×I)Ln+1(1))

Because the odd-dimensional L-groups are trivial one obtains these exact sequences:

0Θ4iΩ4ialmbP4i0
0Θ4i2Ω4i2alm/2bP4i20
0bP2jΘ2j1Ω2j1alm0

The results of Kervaire and Milnor are obtained by studying the middle map in the first two sequences and by relating the groups Ωialm to stable homotopy theory.

2. Topological spheres

The generalized Poincaré conjecture in dimension n can be phrased as saying that 𝒮TOP(Sn)=0. It has been proved for any n by the work of Smale, Freedman and Perelman. From the surgery exact sequence for Sn for n5 in the topological category we see that

θ:𝒩TOP(Sn)Ln(1)

is an isomorphism. (In fact this can be extended to n1 by some ad-hoc methods.)

3. Complex projective spaces in the topological category

The complex projective space Pn is a (2n)-dimensional topological manifold with π1(Pn)=1. In addition it is known that in the case π1(X)=1 in the topological category the surgery obstruction map θ is always surjective. Hence we have

0𝒮TOP(Pn)𝒩TOP(Pn)L2n(1)0

From the work of Sullivan one can calculate

𝒩(Pn)i=1n/2i=1(n+1)/22 and hence 𝒮(Pn)i=1(n1)/2i=1n/22

4. Aspherical manifolds in the topological category

An aspherical n-dimensional manifold X is an n-manifold such that πi(X)=0 for i2. Hence the only non-trivial homotopy group is π1(X)

One way to state the Borel conjecture is to say that for such X we have that the Whitehead group Wh(π1(X)) is trivial and that

𝒮(X)=0

This conjecture was proven in many special cases - for example when π1(X) is n, when it is the fundamental group of a negatively curved manifold or when it is a word-hyperbolic group or a CAT(0)-group.

The statement is equivalent to showing that the surgery obstruction map to the right of the surgery structure set is injective and the surgery obstruction map to the left of the surgery structure set is surjective. Most of the proofs of the above mentioned results are done by studying these maps or by studying the assembly maps with which they can be identified. See more details in Borel conjecture, Farrell-Jones Conjecture.

References

  • Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.

    Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.

    In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.

    Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region

    Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.

    15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.

    To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010
  • Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.

    Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.

    In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.

    Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region

    Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.

    15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.

    To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010
  • Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.

    Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.

    In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.

    Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region

    Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.

    15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.

    To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010
  • Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.

    Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.

    In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.

    Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region

    Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.

    15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.

    To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010
  • Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.

    Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.

    In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.

    Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region

    Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.

    15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.

    To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010