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In the [[mathematics|mathematical]] field of [[order theory]] an '''order isomorphism''' is a special kind of [[monotone function]] that constitutes a suitable notion of [[isomorphism]] for [[partially ordered set]]s (posets). Whenever two posets are order isomorphic, they can be considered to be "essentially the same" in the sense that one of the orders can be obtained from the other just by renaming of elements. Two strictly weaker notions that relate to order isomorphisms are [[order embedding]]s and [[Galois connection]]s.<ref>{{harvtxt|Block|2011}}; {{harvtxt|Ciesielski|1997}}.</ref> | |||
==Definition== | |||
Formally, given two posets <math>(S,\le_S)</math> and <math>(T,\le_T)</math>, an '''order isomorphism''' from <math>(S,\le_S)</math> to <math>(T,\le_T)</math> is a [[bijection|bijective function]] <math>f</math> from <math>S</math> to <math>T</math> with the property that, for every <math>x</math> and <math>y</math> in <math>S</math>, <math>x \le_S y</math> if and only if <math>f(x)\le_T f(y)</math>. That is, it is a bijective [[order-embedding]].<ref>This is the definition used by {{harvtxt|Ciesielski|1997}}. For {{harvtxt|Bloch|2011}} and {{harvtxt|Schröder|2003}} it is a consequence of a different definition.</ref> | |||
It is also possible to define an order isomorphism to be a [[surjective]] order-embedding. The two assumptions that <math>f</math> cover all the elements of <math>T</math> and that it preserve orderings, are enough to ensure that <math>f</math> is also one-to-one, for if <math>f(x)=f(y)</math> then (by the assumption that <math>f</math> preserves the order) it would follow that <math>x\le y</math> and <math>y\le x</math>, implying by the definition of a partial order that <math>x=y</math>. | |||
Yet another characterization of order isomorphisms is that they are exactly the [[monotone function|monotone]] [[bijection]]s that have a monotone inverse.<ref>This is the definition used by {{harvtxt|Bloch|2011}} and {{harvtxt|Schröder|2003}}.</ref> | |||
An order isomorphism from a partially ordered set to itself is called an '''order [[automorphism]]'''.<ref>{{harvtxt|Schröder|2003}}, p. 13.</ref> | |||
==Examples== | |||
* The [[identity function]] on any partially ordered set is always an order automorphism. | |||
* [[Additive inverse|Negation]] is an order isomorphism from <math>(\mathbb{R},\leq)</math> to <math>(\mathbb{R},\geq)</math> (where <math>\mathbb{R}</math> is the set of [[real number]]s and <math>\le</math> denotes the usual numerical comparison), since −''x'' ≥ −''y'' if and only if ''x'' ≤ ''y''.<ref>See example 4 of {{harvtxt|Ciesielski|1997}}, p. 39., for a similar example with integers in place of real numbers.</ref> | |||
* The [[open interval]] <math>(0,1)</math> (again, ordered numerically) does not have an order isomorphism to or from the [[closed interval]] <math>[0,1]</math>: the closed interval has a least element, but the open interval does not, and order isomorphisms must preserve the existence of least elements.<ref>{{harvtxt|Ciesielski|1997}}, example 1, p. 39.</ref> | |||
==Order types== | |||
If <math>f</math> is an order isomorphism, then so is its [[inverse function]]. | |||
Also, if <math>f</math> is an order isomorphism from <math>(S,\le_S)</math> to <math>(T,\le_T)</math> and <math>g</math> is an order isomorphism from <math>(T,\le_T)</math> to <math>(U,\le_U)</math>, then the [[function composition]] of <math>f</math> and <math>g</math> is itself an order isomorphism, from <math>(S,\le_S)</math> to <math>(U,\le_U)</math>.<ref>{{harvtxt|Ciesielski|1997}}; {{harvtxt|Schröder|2003}}.</ref> | |||
Two partially ordered sets are said to be '''order isomorphic''' when there exists an order isomorphism from one to the other.<ref>{{harvtxt|Ciesielski|1997}}.</ref> Identity functions, function inverses, and compositions of functions correspond, respectively, to the three defining characteristics of an [[equivalence relation]]: [[reflexive relation|reflexivity]], [[symmetric relation|symmetry]], and [[transitive relation|transitivity]]. Therefore, order isomorphism is an equivalence relation. The class of partially ordered sets can be partitioned by it into [[equivalence class]]es, families of partially ordered sets that are all isomorphic to each other. These equivalence classes are called [[order type]]s. | |||
==See also== | |||
*[[Permutation pattern]], a permutation that is order-isomorphic to a subsequence of another permutation | |||
==Notes== | |||
{{reflist|colwidth=30em}} | |||
==References== | |||
*{{citation | |||
| last = Bloch | first = Ethan D. | |||
| edition = 2nd | |||
| isbn = 9781441971265 | |||
| pages = 276–277 | |||
| publisher = Springer | |||
| series = Undergraduate Texts in Mathematics | |||
| title = Proofs and Fundamentals: A First Course in Abstract Mathematics | |||
| url = http://books.google.com/books?id=QJ_537n8zKYC&pg=PA276 | |||
| year = 2011}}. | |||
*{{citation | |||
| last = Ciesielski | first = Krzysztof | |||
| isbn = 9780521594653 | |||
| pages = 38–39 | |||
| publisher = Cambridge University Press | |||
| series = London Mathematical Society Student Texts | |||
| title = Set Theory for the Working Mathematician | |||
| url = http://books.google.com/books?id=tTEaMFvzhDAC&pg=PA38 | |||
| volume = 39 | |||
| year = 1997}}. | |||
*{{citation | |||
| last = Schröder | first = Bernd Siegfried Walter | |||
| isbn = 9780817641283 | |||
| page = 11 | |||
| publisher = Springer | |||
| title = Ordered Sets: An Introduction | |||
| url = http://books.google.com/books?id=2esoXnolEWgC&pg=PA11&lpg=PA11 | |||
| year = 2003}}. | |||
[[Category:Order theory]] | |||
[[Category:Morphisms]] |
Revision as of 19:55, 30 January 2014
In the mathematical field of order theory an order isomorphism is a special kind of monotone function that constitutes a suitable notion of isomorphism for partially ordered sets (posets). Whenever two posets are order isomorphic, they can be considered to be "essentially the same" in the sense that one of the orders can be obtained from the other just by renaming of elements. Two strictly weaker notions that relate to order isomorphisms are order embeddings and Galois connections.[1]
Definition
Formally, given two posets and , an order isomorphism from to is a bijective function from to with the property that, for every and in , if and only if . That is, it is a bijective order-embedding.[2]
It is also possible to define an order isomorphism to be a surjective order-embedding. The two assumptions that cover all the elements of and that it preserve orderings, are enough to ensure that is also one-to-one, for if then (by the assumption that preserves the order) it would follow that and , implying by the definition of a partial order that .
Yet another characterization of order isomorphisms is that they are exactly the monotone bijections that have a monotone inverse.[3]
An order isomorphism from a partially ordered set to itself is called an order automorphism.[4]
Examples
- The identity function on any partially ordered set is always an order automorphism.
- Negation is an order isomorphism from to (where is the set of real numbers and denotes the usual numerical comparison), since −x ≥ −y if and only if x ≤ y.[5]
- The open interval (again, ordered numerically) does not have an order isomorphism to or from the closed interval : the closed interval has a least element, but the open interval does not, and order isomorphisms must preserve the existence of least elements.[6]
Order types
If is an order isomorphism, then so is its inverse function. Also, if is an order isomorphism from to and is an order isomorphism from to , then the function composition of and is itself an order isomorphism, from to .[7]
Two partially ordered sets are said to be order isomorphic when there exists an order isomorphism from one to the other.[8] Identity functions, function inverses, and compositions of functions correspond, respectively, to the three defining characteristics of an equivalence relation: reflexivity, symmetry, and transitivity. Therefore, order isomorphism is an equivalence relation. The class of partially ordered sets can be partitioned by it into equivalence classes, families of partially ordered sets that are all isomorphic to each other. These equivalence classes are called order types.
See also
- Permutation pattern, a permutation that is order-isomorphic to a subsequence of another permutation
Notes
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References
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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.
- ↑ Template:Harvtxt; Template:Harvtxt.
- ↑ This is the definition used by Template:Harvtxt. For Template:Harvtxt and Template:Harvtxt it is a consequence of a different definition.
- ↑ This is the definition used by Template:Harvtxt and Template:Harvtxt.
- ↑ Template:Harvtxt, p. 13.
- ↑ See example 4 of Template:Harvtxt, p. 39., for a similar example with integers in place of real numbers.
- ↑ Template:Harvtxt, example 1, p. 39.
- ↑ Template:Harvtxt; Template:Harvtxt.
- ↑ Template:Harvtxt.