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{{DISPLAYTITLE:C<sub>0</sub>-semigroup }}
In [[mathematics]], a '''''C''<sub>0</sub>-semigroup''', also known as a '''strongly continuous one-parameter semigroup''', is a generalization of the [[exponential function]]. Just as exponential functions provide solutions of scalar linear constant coefficient [[ordinary differential equation]]s, strongly continuous [[semigroup]]s provide solutions of linear constant coefficient ordinary differential equations in [[Banach space]]s. Such differential equations in Banach spaces arise from e.g. [[delay differential equation]]s and [[partial differential equation]]s.
 
Formally, a strongly continuous semigroup is a representation of the semigroup ('''R'''<sub>+</sub>,+) on some [[Banach space]] ''X'' that is continuous in the [[strong operator topology]]. Thus, strictly speaking, a strongly continuous semigroup is not a semigroup, but rather a continuous representation of a very particular semigroup.
 
== Formal definition ==
A '''strongly continuous semigroup''' on a [[Banach space]] <math>X</math> is a map
<math> T : \mathbb{R}_+ \to  L(X) </math>
such that
# <math> T(0) = I </math>, &nbsp; ([[identity operator]] on <math>X</math>)
# <math>\forall t,s \ge 0 : \ T(t + s) = T(t) T(s)</math>
# <math>\forall x_0 \in X: \ \|T(t) x_0 - x_0\| \to 0</math>, as <math>t\downarrow 0</math>.
The first two axioms are algebraic, and state that <math>T</math> is a representation of the semigroup (<math>\mathbb{R}_+,+</math>); the last is topological, and states that the map <math>T</math> is [[Continuity (topology)|continuous]] in the [[strong operator topology]].
 
== Elementary examples ==
Let ''A'' be a [[bounded operator]] on the [[Banach space]] ''X'', then
 
:<math>T(t)={\rm e}^{At}:=\sum_{k=0}^\infty\frac{A^k}{k!}t^k</math>
 
is a strongly continuous semigroup (it is even continuous in the [[uniform operator topology]]). Conversely,<ref name="Engeland">Engel and Nagel Theorem I.3.7</ref> any uniformly continuous semigroup is necessarily of this form for some [[bounded linear operator]] ''A''. In particular,<ref>Engel and Nagel Theorem I.2.9</ref> if ''X'' is a finite-dimensional Banach space, then any strongly continuous semigroup is necessarily of this form for some [[linear operator]] ''A''.
 
== Infinitesimal generator ==
 
The '''infinitesimal generator''' ''A'' of a strongly continuous semigroup ''T'' is defined by
 
: <math> A\,x = \lim_{t\downarrow0} \frac1t\,(T(t)- I)\,x </math>
 
whenever the limit exists. The domain of ''A'', ''D''(''A''), is the set of ''x&isin;X'' for which this limit does exist; ''D''(''A'') is a linear subspace and ''A'' is linear on this domain.<ref>Partington (2004) page 23</ref>  The operator ''A'' is [[Closed operator|closed]], although not necessarily [[Bounded operator|bounded]], and the domain is dense in ''X''.<ref>Partington (2004) page 24</ref>
 
The strongly continuous semigroup ''T'' with generator ''A''  is often denoted by the symbol ''e<sup>At</sup>''. This notation is compatible with the notation for [[matrix exponential]]s, and for functions of an operator defined via [[functional calculus]] (for example, via the [[spectral theorem]]).
 
==Abstract Cauchy problems==
Consider the abstract [[Cauchy problem]]:
:<math>u'(t)=Au(t),~~~u(0)=x,</math>
 
where ''A'' is a [[closed operator]] on a [[Banach space]] ''X'' and ''x∈X''. There are two concepts of solution of this problem:
* a continuously differentiable function ''u:[0,&infin;)→X'' is called a '''classical solution''' of the Cauchy problem if ''u''(''t'') ∈ ''D''(''A'') for all ''t'' ≥ 0 and it satisfies the initial value problem,
* a continuous function ''u'':[0,∞) → ''X'' is called a '''mild solution''' of the Cauchy problem if
 
:<math>\int_0^t u(s)\,ds\in D(A)\text{ and }A \int_0^t u(s)\,ds=u(t)-x.</math>
 
Any classical solution is a mild solution. A mild solution is a classical solution if and only if it is continuously differentiable.<ref>Arendt et. al. Proposition 3.1.2</ref>
 
The following theorem connects abstract Cauchy problems and strongly continuous semigroups.
 
'''Theorem<ref>Arendt et. al. Theorem 3.1.12</ref>''' Let ''A'' be a closed operator on a Banach space ''X''. The following assertions are equivalent:
# for all ''x&isin;X'' there exists a unique mild solution of the abstract Cauchy problem,
# the operator ''A'' generates a strongly continuous semigroup,
# the [[resolvent set]] of ''A'' is nonempty and for all ''x'' ∈ ''D''(''A'') there exists a unique classical solution of the Cauchy problem.
When these assertions hold, the solution of the Cauchy problem is given by ''u''(''t'')&nbsp;=&nbsp;''T''(''t'')''x'' with ''T'' the strongly continuous semigroup generated by ''A''.
 
== Generation theorems ==
In connection with Cauchy problems, usually a [[linear operator]] ''A'' is given and the question is whether this is the generator of a strongly continuous semigroup. Theorems which answer this question are called '''generation theorems'''. A complete characterization of operators that generate strongly continuous semigroups is given by the [[Hille-Yosida theorem]]. Of more practical importance are however the much easier to verify conditions given by the [[Lumer-Phillips theorem]].
 
== Special classes of semigroups ==
 
===Uniformly continuous semigroups===
The strongly continuous semigroup ''T'' is called '''uniformly continuous''' if the map ''t''&nbsp;→&nbsp;''T''(''t'') is continuous from [0,&nbsp;∞) to ''L''(''X'').
 
The generator of a uniformly continuous semigroup is a [[bounded operator]].<ref name="Engeland" />
 
===Analytic semigroups===
{{Main|analytic semigroup}}
 
===Contraction semigroups===
{{Main|contraction semigroup}}
 
===Differentiable semigroups===
A strongly continuous semigroup ''T'' is called '''eventually differentiable''' if there exists a ''t''<sub>0</sub>&nbsp;>&nbsp;0 such that ''T(t<sub>0</sub>)X⊂D(A)'' (equivalently: ''T''(''t'')''X'' ⊂ ''D''(''A'') for all ''t''&nbsp;≥&nbsp;''t''<sub>0</sub>) and ''T'' is '''immediately differentiable''' if ''T''(''t'')''X''&nbsp;⊂&nbsp;''D''(''A'') for all ''t''&nbsp;>&nbsp;0.
 
Every analytic semigroup is immediately differentiable.
 
An equivalent characterization in terms of Cauchy problems is the following: the strongly continuous semigroup generated by ''A'' is eventually differentiable if and only if there exists a ''t''<sub>1</sub>&nbsp;≥&nbsp;0 such that for all ''x''&nbsp;∈&nbsp;''X'' the solution ''u'' of the abstract Cauchy problem is differentiable on (''t''<sub>1</sub>,&nbsp;∞). The semigroup is immediately differentiable if ''t''<sub>1</sub> can be chosen to be zero.
 
===Compact semigroups===
A strongly continuous semigroup ''T'' is called '''eventually compact''' if there exists a ''t''<sub>0</sub>&nbsp;>&nbsp;0 such that ''T''(''t''<sub>0</sub>) is a [[compact operator]] (equivalently<ref>Engel and Nagel Lemma II.4.22</ref> if ''T''(''t'') is a compact operator for all ''t''&nbsp;≥&nbsp;''t''<sub>0</sub>) . The semigroup is called '''immediately compact''' if ''T''(''t'') is a compact operator for all ''t''&nbsp;>&nbsp;0.
 
===Norm continuous semigroups===
A strongly continuous semigroup is called '''eventually norm continuous''' if there exists a ''t''<sub>0</sub>&nbsp;≥&nbsp;0 such that the map ''t''&nbsp;→&nbsp;''T''(''t'') is continuous from (''t''<sub>0</sub>,&nbsp;∞) to ''L''(''X''). The semigroup is called '''immediately norm continuous''' if ''t''<sub>0</sub> can be chosen to be zero.  
 
Note that for an immediately norm continuous semigroup the map ''t''&nbsp;→&nbsp;''T''(''t'') may not be continuous in ''t''&nbsp;=&nbsp;0 (that would make the semigroup uniformly continuous).
 
Analytic semigroups, (eventually) differentiable semigroups and (eventually) compact semigroups are all eventually norm continuous.<ref>Engel and Nagel (diagram II.4.26)</ref>
 
== Stability ==
 
===Exponential stability===
 
The '''growth bound''' of a semigroup ''T'' is the constant
 
: <math> \omega_0 = \lim_{t\downarrow0} \frac1t \log \| T(t) \|. </math>
 
It is so called as this number is also the infimum of all real numbers ''&omega;'' such that there exists a constant ''M''  (≥&nbsp;1) with
 
: <math>\|T(t)\| \leq Me^{\omega t}</math>
 
for all ''t'' ≥ 0.
 
The following are equivalent:<ref>Engel and Nagel Section V.1.b</ref>
#There exist M,ω>0 such that for all ''t''&nbsp;≥&nbsp;0:  <math>\|T(t)\|\leq M{\rm e}^{-\omega t},</math>
#The growth bound is negative: ''&omega;''<sub>0</sub>&nbsp;<&nbsp;0,
#The semigroup converges to zero in the [[uniform operator topology]]: <math>\lim_{t\to\infty}\|T(t)\|=0</math>,
#There exists a ''t''<sub>0</sub>&nbsp;>&nbsp;0 such that <math>\|T(t_0)\|<1</math>,
#There exists a ''t''<sub>1</sub>&nbsp;>&nbsp;0 such that the [[spectral radius]] of ''T''(''t''<sub>1</sub>) is strictly smaller than 1,
#There exists a ''p''&nbsp;∈&nbsp;[1,&nbsp;∞) such that for all ''x∈X'': <math>\int_0^\infty\|T(t)x\|^p\,dt<\infty</math>,
#For all ''p''&nbsp;∈&nbsp;[1,&nbsp;∞) and all ''x''&nbsp;∈&nbsp;''X'': <math>\int_0^\infty\|T(t)x\|^p\,dt<\infty.</math>
 
A semigroup that satisfies these equivalent conditions is called '''exponentially stable''' or '''uniformly stable''' (either of the first three of the above statements is taken as the definition in certain parts of the literature). That the ''L<sup>p</sup>'' conditions are equivalent to exponential stability is called the '''Datko-Pazy theorem'''.  
 
In case ''X'' is a [[Hilbert space]] there is another condition that is equivalent to exponential stability in terms of the [[resolvent operator]] of the generator:<ref>Engel and Nagel Theorem V.1.11</ref> all ''λ'' with positive real part belong to the resolvent set of ''A'' and the resolvent operator is uniformly bounded on the right half plane, i.e. (''λI''&nbsp;&minus;&nbsp;''A'')<sup>&minus;1</sup> belongs to the [[Hardy space]] <math>H^\infty(\mathbb{C}_+;L(X))</math>. This is called the '''Gearhart-Pruss theorem'''.
 
The '''spectral bound''' of an operator ''A'' is the constant
:<math>s(A):=\sup\{{\rm Re}\lambda:\lambda\in\sigma(A)\}</math>,
with the convention that ''s''(''A'')&nbsp;=&nbsp;&minus;∞ if the [[spectrum]] of ''A'' is empty.
 
The growth bound of a semigroup and the spectral bound of its generator are related by:<ref>Engel and Nagel Proposition IV2.2</ref> ''s(A)≤&omega;<sub>0</sub>(T)''. There are examples<ref>Engel and Nagel Section IV.2.7, Luo et. al. Example 3.6</ref> where ''s''(''A'')&nbsp;<&nbsp;''ω''<sub>0</sub>(''T''). If ''s''(''A'')&nbsp;=&nbsp;''&omega;''<sub>0</sub>(''T''), then ''T'' is said to satisfy the '''spectral determined growth condition'''. Eventually norm-continuous semigroups satisfy the spectral determined growth condition.<ref>Engel and Nagel Corollary 4.3.11</ref> This gives another equivalent characterization of exponential stability for these semigroups:
*An eventually norm-continuous semigroup is exponentially stable if and only if ''s''(''A'')&nbsp;<&nbsp;0.
Note that eventually compact, eventually differentiable, analytic and uniformly continuous semigroups are eventually norm-continuous so that the spectral determined growth condition holds in particular for those semigroups.
 
=== Strong stability ===
A strongly continuous semigroup ''T'' is called '''strongly stable''' or '''asymptotically stable''' if for all ''x''&nbsp;∈&nbsp;''X'': <math>\lim_{t\to\infty}\|T(t)x\|=0</math>.
 
Exponential stability implies strong stability, but the converse is not generally true if ''X'' is infinite-dimensional (it is true for ''X'' finite-dimensional).
 
The following sufficient condition for strong stability is called the '''Arendt-Batty-Lyubich-Phong theorem''':<ref>Arendt and Batty, Lyubich and Phong</ref> Assume that
# ''T'' is bounded: there exists a ''M''&nbsp;≥&nbsp;1 such that <math>\|T(t)\|\leq M</math>,
# ''A'' has not [[residual spectrum]] on the imaginary axis, and
# The spectrum of ''A'' located on the imaginary axis is countable.
Then ''T'' is strongly stable.
 
If ''X'' is reflexive then the conditions simplify: if ''T'' is bounded, ''A'' has no eigenvalues on the imaginary axis and the spectrum of ''A'' located on the imaginary axis is countable, then ''T'' is strongly stable.
 
== See also ==
* [[Hille&ndash;Yosida theorem]]
* [[Lumer&ndash;Phillips theorem]]
* [[Analytic semigroup]]
* [[Contraction semigroup]]
* [[Matrix exponential]]
* [[Strongly continuous family of operators]]
 
==Notes==
 
{{reflist|2}}
 
== References ==
* E Hille, R S Phillips: ''Functional Analysis and Semi-Groups''. American Mathematical Society, 1975.
* R F Curtain, H J Zwart: ''An introduction to infinite dimensional linear systems theory''. Springer Verlag, 1995.
* [[E. Brian Davies|E.B. Davies]]: ''One-parameter semigroups'' (L.M.S. monographs), Academic Press, 1980, ISBN 0-12-206280-9.
*{{ citation | last1=Engel| first1=Klaus-Jochen| last2=Nagel| first2=Rainer | title=One-parameter semigroups for linear evolution equations | year=2000| publisher=Springer}}
*{{ citation | last1=Arendt| first1=Wolfgang| last2=Batty| first2=Charles | last3=Hieber| first3=Matthias| last4=Neubrander| first4=Frank |title=Vector-valued Laplace Transforms and Cauchy Problems | year=2001| publisher=Birkhauser}}
*{{ citation | last1=Staffans| first1=Olof| title=Well-posed linear systems | year=2005| publisher=Cambridge University Press}}
*{{ citation | last1=Luo| first1=Zheng-Hua| last2=Guo| first2=Bao-Zhu | last3=Morgul| first3=Omer |title=Stability and Stabilization of Infinite Dimensional Systems with Applications | year=1999| publisher=Springer}}
*{{ citation | last1=Arendt| first1=Wolfgang| last2=Batty| first2=Charles| title=Tauberian theorems and stability of one-parameter semigroups | year=1988| publisher=Transactions of the American mathematical society}}
*{{ citation | last1=Lyubich| first1=Yu| last2=Phong| first2=Vu Quoc| title=Asymptotic stability of linear differential equations in Banach spaces | year=1988| publisher=Studia Mathematica}}
*{{ citation | last=Partington | first=Jonathan R. | authorlink=Jonathan Partington | title=Linear operators and linear systems | series=[[London Mathematical Society]] Student Texts | issue=60 | publisher=[[Cambridge University Press]] | isbn=0-521-54619-2 | year=2004 }}
 
{{DEFAULTSORT:C0-Semigroup}}
[[Category:Functional analysis]]
[[Category:Semigroup theory]]

Revision as of 01:48, 1 January 2014

In mathematics, a C0-semigroup, also known as a strongly continuous one-parameter semigroup, is a generalization of the exponential function. Just as exponential functions provide solutions of scalar linear constant coefficient ordinary differential equations, strongly continuous semigroups provide solutions of linear constant coefficient ordinary differential equations in Banach spaces. Such differential equations in Banach spaces arise from e.g. delay differential equations and partial differential equations.

Formally, a strongly continuous semigroup is a representation of the semigroup (R+,+) on some Banach space X that is continuous in the strong operator topology. Thus, strictly speaking, a strongly continuous semigroup is not a semigroup, but rather a continuous representation of a very particular semigroup.

Formal definition

A strongly continuous semigroup on a Banach space X is a map T:+L(X) such that

  1. T(0)=I,   (identity operator on X)
  2. t,s0:T(t+s)=T(t)T(s)
  3. x0X:T(t)x0x00, as t0.

The first two axioms are algebraic, and state that T is a representation of the semigroup (+,+); the last is topological, and states that the map T is continuous in the strong operator topology.

Elementary examples

Let A be a bounded operator on the Banach space X, then

T(t)=eAt:=k=0Akk!tk

is a strongly continuous semigroup (it is even continuous in the uniform operator topology). Conversely,[1] any uniformly continuous semigroup is necessarily of this form for some bounded linear operator A. In particular,[2] if X is a finite-dimensional Banach space, then any strongly continuous semigroup is necessarily of this form for some linear operator A.

Infinitesimal generator

The infinitesimal generator A of a strongly continuous semigroup T is defined by

Ax=limt01t(T(t)I)x

whenever the limit exists. The domain of A, D(A), is the set of x∈X for which this limit does exist; D(A) is a linear subspace and A is linear on this domain.[3] The operator A is closed, although not necessarily bounded, and the domain is dense in X.[4]

The strongly continuous semigroup T with generator A is often denoted by the symbol eAt. This notation is compatible with the notation for matrix exponentials, and for functions of an operator defined via functional calculus (for example, via the spectral theorem).

Abstract Cauchy problems

Consider the abstract Cauchy problem:

u(t)=Au(t),u(0)=x,

where A is a closed operator on a Banach space X and x∈X. There are two concepts of solution of this problem:

  • a continuously differentiable function u:[0,∞)→X is called a classical solution of the Cauchy problem if u(t) ∈ D(A) for all t ≥ 0 and it satisfies the initial value problem,
  • a continuous function u:[0,∞) → X is called a mild solution of the Cauchy problem if
0tu(s)dsD(A) and A0tu(s)ds=u(t)x.

Any classical solution is a mild solution. A mild solution is a classical solution if and only if it is continuously differentiable.[5]

The following theorem connects abstract Cauchy problems and strongly continuous semigroups.

Theorem[6] Let A be a closed operator on a Banach space X. The following assertions are equivalent:

  1. for all x∈X there exists a unique mild solution of the abstract Cauchy problem,
  2. the operator A generates a strongly continuous semigroup,
  3. the resolvent set of A is nonempty and for all xD(A) there exists a unique classical solution of the Cauchy problem.

When these assertions hold, the solution of the Cauchy problem is given by u(t) = T(t)x with T the strongly continuous semigroup generated by A.

Generation theorems

In connection with Cauchy problems, usually a linear operator A is given and the question is whether this is the generator of a strongly continuous semigroup. Theorems which answer this question are called generation theorems. A complete characterization of operators that generate strongly continuous semigroups is given by the Hille-Yosida theorem. Of more practical importance are however the much easier to verify conditions given by the Lumer-Phillips theorem.

Special classes of semigroups

Uniformly continuous semigroups

The strongly continuous semigroup T is called uniformly continuous if the map t → T(t) is continuous from [0, ∞) to L(X).

The generator of a uniformly continuous semigroup is a bounded operator.[1]

Analytic semigroups

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Contraction semigroups

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Differentiable semigroups

A strongly continuous semigroup T is called eventually differentiable if there exists a t0 > 0 such that T(t0)X⊂D(A) (equivalently: T(t)XD(A) for all t ≥ t0) and T is immediately differentiable if T(t)X ⊂ D(A) for all t > 0.

Every analytic semigroup is immediately differentiable.

An equivalent characterization in terms of Cauchy problems is the following: the strongly continuous semigroup generated by A is eventually differentiable if and only if there exists a t1 ≥ 0 such that for all x ∈ X the solution u of the abstract Cauchy problem is differentiable on (t1, ∞). The semigroup is immediately differentiable if t1 can be chosen to be zero.

Compact semigroups

A strongly continuous semigroup T is called eventually compact if there exists a t0 > 0 such that T(t0) is a compact operator (equivalently[7] if T(t) is a compact operator for all t ≥ t0) . The semigroup is called immediately compact if T(t) is a compact operator for all t > 0.

Norm continuous semigroups

A strongly continuous semigroup is called eventually norm continuous if there exists a t0 ≥ 0 such that the map t → T(t) is continuous from (t0, ∞) to L(X). The semigroup is called immediately norm continuous if t0 can be chosen to be zero.

Note that for an immediately norm continuous semigroup the map t → T(t) may not be continuous in t = 0 (that would make the semigroup uniformly continuous).

Analytic semigroups, (eventually) differentiable semigroups and (eventually) compact semigroups are all eventually norm continuous.[8]

Stability

Exponential stability

The growth bound of a semigroup T is the constant

ω0=limt01tlogT(t).

It is so called as this number is also the infimum of all real numbers ω such that there exists a constant M (≥ 1) with

T(t)Meωt

for all t ≥ 0.

The following are equivalent:[9]

  1. There exist M,ω>0 such that for all t ≥ 0: T(t)Meωt,
  2. The growth bound is negative: ω0 < 0,
  3. The semigroup converges to zero in the uniform operator topology: limtT(t)=0,
  4. There exists a t0 > 0 such that T(t0)<1,
  5. There exists a t1 > 0 such that the spectral radius of T(t1) is strictly smaller than 1,
  6. There exists a p ∈ [1, ∞) such that for all x∈X: 0T(t)xpdt<,
  7. For all p ∈ [1, ∞) and all x ∈ X: 0T(t)xpdt<.

A semigroup that satisfies these equivalent conditions is called exponentially stable or uniformly stable (either of the first three of the above statements is taken as the definition in certain parts of the literature). That the Lp conditions are equivalent to exponential stability is called the Datko-Pazy theorem.

In case X is a Hilbert space there is another condition that is equivalent to exponential stability in terms of the resolvent operator of the generator:[10] all λ with positive real part belong to the resolvent set of A and the resolvent operator is uniformly bounded on the right half plane, i.e. (λI − A)−1 belongs to the Hardy space H(+;L(X)). This is called the Gearhart-Pruss theorem.

The spectral bound of an operator A is the constant

s(A):=sup{Reλ:λσ(A)},

with the convention that s(A) = −∞ if the spectrum of A is empty.

The growth bound of a semigroup and the spectral bound of its generator are related by:[11] s(A)≤ω0(T). There are examples[12] where s(A) < ω0(T). If s(A) = ω0(T), then T is said to satisfy the spectral determined growth condition. Eventually norm-continuous semigroups satisfy the spectral determined growth condition.[13] This gives another equivalent characterization of exponential stability for these semigroups:

  • An eventually norm-continuous semigroup is exponentially stable if and only if s(A) < 0.

Note that eventually compact, eventually differentiable, analytic and uniformly continuous semigroups are eventually norm-continuous so that the spectral determined growth condition holds in particular for those semigroups.

Strong stability

A strongly continuous semigroup T is called strongly stable or asymptotically stable if for all x ∈ X: limtT(t)x=0.

Exponential stability implies strong stability, but the converse is not generally true if X is infinite-dimensional (it is true for X finite-dimensional).

The following sufficient condition for strong stability is called the Arendt-Batty-Lyubich-Phong theorem:[14] Assume that

  1. T is bounded: there exists a M ≥ 1 such that T(t)M,
  2. A has not residual spectrum on the imaginary axis, and
  3. The spectrum of A located on the imaginary axis is countable.

Then T is strongly stable.

If X is reflexive then the conditions simplify: if T is bounded, A has no eigenvalues on the imaginary axis and the spectrum of A located on the imaginary axis is countable, then T is strongly stable.

See also

Notes

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References

  • E Hille, R S Phillips: Functional Analysis and Semi-Groups. American Mathematical Society, 1975.
  • R F Curtain, H J Zwart: An introduction to infinite dimensional linear systems theory. Springer Verlag, 1995.
  • E.B. Davies: One-parameter semigroups (L.M.S. monographs), Academic Press, 1980, ISBN 0-12-206280-9.
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    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
  • 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
  1. 1.0 1.1 Engel and Nagel Theorem I.3.7
  2. Engel and Nagel Theorem I.2.9
  3. Partington (2004) page 23
  4. Partington (2004) page 24
  5. Arendt et. al. Proposition 3.1.2
  6. Arendt et. al. Theorem 3.1.12
  7. Engel and Nagel Lemma II.4.22
  8. Engel and Nagel (diagram II.4.26)
  9. Engel and Nagel Section V.1.b
  10. Engel and Nagel Theorem V.1.11
  11. Engel and Nagel Proposition IV2.2
  12. Engel and Nagel Section IV.2.7, Luo et. al. Example 3.6
  13. Engel and Nagel Corollary 4.3.11
  14. Arendt and Batty, Lyubich and Phong