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In mathematics, '''canonical singularities''' appear as singularities of the [[canonical model]] of a [[projective variety]], and '''terminal singularities''' are special cases that appear as singularities of [[Minimal model program|minimal models]]. They were introduced by {{harvtxt|Reid|1980}}. Terminal singularities are important in the [[minimal model program]] because smooth minimal models do not always exist, and thus one must allow certain singularities, namely the terminal singularities. | |||
==Definition== | |||
Suppose that ''Y'' is a normal variety such that its canonical class ''K''<sub>''Y''</sub> is '''Q'''-Cartier, and let ''f'':''X''→''Y'' be a resolution of the singularities of ''Y''. | |||
Then | |||
:<math>\displaystyle K_X = f^*(K_Y)+\sum_i a_iE_i</math> | |||
where the sum is over the irreducible exceptional divisors, and the ''a''<sub>''i''</sub> are rational numbers, called the discrepancies. | |||
Then the singularities of ''Y'' are called: | |||
:'''terminal''' if ''a''<sub>''i''</sub> > 0 for all ''i'' | |||
:'''canonical''' if ''a''<sub>''i''</sub> ≥ 0 for all ''i'' | |||
:'''log terminal''' if ''a''<sub>''i''</sub> > −1 for all ''i'' | |||
:'''log canonical''' if ''a''<sub>''i''</sub> ≥ −1 for all ''i''. | |||
==Properties== | |||
The singularities of a projective variety ''V'' are canonical if the variety is [[normal variety|normal]], some power of the [[canonical line bundle]] of the non-singular part of ''V'' extends to a line bundle on ''V'', and ''V'' has the same [[plurigenera]] as any [[resolution of singularities|resolution]] of its singularities. ''V'' has canonical singularities if and only if it is a [[relative canonical model]]. | |||
The singularities of a projective variety ''V'' are terminal if the variety is [[normal variety|normal]], some power of the [[canonical line bundle]] of the non-singular part of ''V'' extends to a line bundle on ''V'', and ''V'' the pullback of any section of ''V''<sup>''m''</sup> vanishes along any codimension 1 component of the [[exceptional locus]] of a [[resolution of singularities|resolution]] of its singularities. | |||
==Classification in small dimensions== | |||
Two dimensional terminal singularities are smooth. | |||
If a variety has terminal singularities, then its singular points have codimension at least 3, and in particular in dimensions 1 and 2 all terminal singularities are smooth. In 3 dimensions they are isolated and were classified by {{harvtxt|Mori|1985}}. | |||
Two dimensional canonical singularities are the same as [[du Val singularity|du Val singularities]], and are analytically isomorphic to quotients | |||
of '''C'''<sup>2</sup> by finite subgroups of SL<sub>2</sub>('''C'''). | |||
Two dimensional log terminal singularities are analytically isomorphic to quotients | |||
of '''C'''<sup>2</sup> by finite subgroups of GL<sub>2</sub>('''C'''). | |||
Two dimensional log canonical singularities have been classified by {{harvtxt|Kawamata|1988}}. | |||
==Pairs== | |||
More generally one can define these concepts for a pair (''X'',Δ) where Δ is a formal linear combination of prime divisors with rational coefficients. The pair is called | |||
*'''terminal''' if Discrep(''X'',Δ) >0 | |||
*'''canonical''' if Discrep(''X'',Δ) ≥0 | |||
*'''klt''' (Kawamata log terminal) if Discrep(''X'',Δ) >− 1 and |Δ|≤0 | |||
*'''plt''' (purely log terminal) if Discrep(''X'',Δ) >− 1 | |||
*'''lc''' (log canonical) if Discrep(''X'',Δ) ≥− 1. | |||
==References== | |||
*{{Citation | last1=Kollár | first1=János | title=Minimal models of algebraic threefolds: Mori's program | url=http://www.numdam.org/item?id=SB_1988-1989__31__303_0 | mr=1040578 | year=1989 | journal=Astérisque | issn=0303-1179 | issue=177 | pages=303–326}} | |||
*{{Citation | authorlink1=Shigefumi Mori | last1=Mori | first1=Shigefumi | title=On 3-dimensional terminal singularities | url=http://projecteuclid.org/euclid.nmj/1118787793 | mr=792770 | year=1985 | journal=Nagoya Mathematical Journal | issn=0027-7630 | volume=98 | pages=43–66}} | |||
*{{Citation | last1=Reid | first1=Miles | author1-link=Miles Reid | title=Journées de Géometrie Algébrique d'Angers, Juillet 1979/Algebraic Geometry, Angers, 1979 | publisher=Sijthoff & Noordhoff | location=Alphen aan den Rijn | mr=605348 | year=1980 | chapter=Canonical 3-folds | pages=273–310}} | |||
*{{Citation | last1=Reid | first1=Miles | author1-link=Miles Reid | title=Algebraic geometry, Bowdoin, 1985 (Brunswick, Maine, 1985) | publisher=[[American Mathematical Society]] | location=Providence, R.I. | series=Proc. Sympos. Pure Math. | mr=927963 | year=1987 | volume=46 | chapter=Young person's guide to canonical singularities | pages=345–414}} | |||
[[Category:Singularity theory]] | |||
[[Category:Algebraic geometry]] | |||
Revision as of 20:29, 29 October 2013
In mathematics, canonical singularities appear as singularities of the canonical model of a projective variety, and terminal singularities are special cases that appear as singularities of minimal models. They were introduced by Template:Harvtxt. Terminal singularities are important in the minimal model program because smooth minimal models do not always exist, and thus one must allow certain singularities, namely the terminal singularities.
Definition
Suppose that Y is a normal variety such that its canonical class KY is Q-Cartier, and let f:X→Y be a resolution of the singularities of Y. Then
where the sum is over the irreducible exceptional divisors, and the ai are rational numbers, called the discrepancies.
Then the singularities of Y are called:
- terminal if ai > 0 for all i
- canonical if ai ≥ 0 for all i
- log terminal if ai > −1 for all i
- log canonical if ai ≥ −1 for all i.
Properties
The singularities of a projective variety V are canonical if the variety is normal, some power of the canonical line bundle of the non-singular part of V extends to a line bundle on V, and V has the same plurigenera as any resolution of its singularities. V has canonical singularities if and only if it is a relative canonical model.
The singularities of a projective variety V are terminal if the variety is normal, some power of the canonical line bundle of the non-singular part of V extends to a line bundle on V, and V the pullback of any section of Vm vanishes along any codimension 1 component of the exceptional locus of a resolution of its singularities.
Classification in small dimensions
Two dimensional terminal singularities are smooth. If a variety has terminal singularities, then its singular points have codimension at least 3, and in particular in dimensions 1 and 2 all terminal singularities are smooth. In 3 dimensions they are isolated and were classified by Template:Harvtxt.
Two dimensional canonical singularities are the same as du Val singularities, and are analytically isomorphic to quotients of C2 by finite subgroups of SL2(C).
Two dimensional log terminal singularities are analytically isomorphic to quotients of C2 by finite subgroups of GL2(C).
Two dimensional log canonical singularities have been classified by Template:Harvtxt.
Pairs
More generally one can define these concepts for a pair (X,Δ) where Δ is a formal linear combination of prime divisors with rational coefficients. The pair is called
- terminal if Discrep(X,Δ) >0
- canonical if Discrep(X,Δ) ≥0
- klt (Kawamata log terminal) if Discrep(X,Δ) >− 1 and |Δ|≤0
- plt (purely log terminal) if Discrep(X,Δ) >− 1
- lc (log canonical) if Discrep(X,Δ) ≥− 1.
References
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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