# 3.3 Nonstandard interpretations (optional)  (Page 2/2)

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The critical point of his interpretation of a non-Euclidean geometry is this: it is embedded in Euclidean geometry! So we are able to prove (within the embedding Euclidean geometry) that the disc-postulates hold ( e.g. , we can prove the statement [*]above as a theorem about circular arcs in Euclidean geometry).Therefore, if there is any inconsistency in non-Euclidean geometry, then that could be parlayed into some inconsistency of Euclidean geometry.Thus, his interpretation gives a proof that the strange non-Euclidean geometryis as sound as our familiar Euclidean geometry.

## P vs. np and oracles

A well-known problem in computer scienceP vs. NPasks whether (for a given problem) it is truly moredifficult to find a short solution (when one exists) (NP), than it is to verify a short purported solution handed to you(P). For example,Given a set of people and how strong person is, can you partition them into two tug-of-war teamswhich are exactly evenly matched?Certainly it seems easier to check that a pair of proposed rosters has equal strength(and, verify that everybody really is on one team or the other)than to have to come up with two perfectly-matched teams. But conceivably, the two tasks might be equally-difficultup to some acceptable (polynomial time) overhead. While every assumes that P is easier than NP,nobody has been able to prove it.

An interesting variant of the problem lets both the problem-solver and the purported-answer-verifier each have access toa particular oracle a program that will gives instant yes/no answers to some other problem (say,given any set of numbers, yes or no: is there an even-sized subsetwhose total is exactly the same as some odd sized subset?).

It has been shown that there is some oracle which makes theproblem-solver's job provably tougher than the proof-verifier's job, and also there is some other oracleproblem-solver's job provably no-tougher than the proof-verifier's job.

This means that any proof of P being different from NP has to be subtle enough so thatwhen P and NP are re-interpreted asP and NP with respect to a particular oracle, the proof will no longer go through.Unfortunately, this eliminates all the routine methods of proof; we know that solving this problem will take some new attack.

## LWenheim-skolem and the real numbers

The Lwenheim-Skolem theorem of logic states that if a set of (countable) domain axioms has a model at all,then it has a countable model. This is a bit surprising when applied to the axioms ofarithmetic for the real numbers: even though the real numbers are uncountable,there is some countable model which meets all our (finite) axioms of the real numbers!

## Object-oriented programming

Note that object-oriented programming is founded on the possibility for nonstandard interpretations:perhaps you have some code which is given a list of `Object` s, and you proceed to call the method `toString` on each of them. Certainly there is a standard interpretation for the function `Object.toString` , but your code is built to work even when you call this function andsome nonstandard, custom, overridden method is called instead.

It can become very difficult to reason about programs when the run-time method invoked might be different from the one being called.We're used to specifying type constratins which any interpretation must satisfy;wouldn't it be nice to specify more complicated constraints, e.g. this function returns an `int` which is a valid index into [some array]? And if we can describe the constraint formally (rather than in English comments, which is how most code works), then we could have the computer enforce that contract!(for every interpretation which gets executed, including non-static ones).

An obvious formal specification language is code itselfhave code which verifies pre-conditions before calling a function,and then runs code verifying the post-condition before leaving the function. Indeed,there are several such tools about ( Java , Scheme ). In the presence of inheritance, it's harder than you might initially think todo this correctly .

It is still a research goal to be able to (sometimes) optimize away such run-time verifications;this requires proving that some code is correct (at least, with respect to its post-condition).The fact that the code might call a function which will be later overridden (ournon-standard interpretations) exacerbates this difficulty.(And proving correctness in the presence of concurrency is even tougher!)

Even if not proving programs correct, being able to specify contracts in a formallanguage (code or logic) is a valuable skill.

## Real-world arguments

Finally, it is worth noting that many rebuttles of real world arguments (see also some exercises ) amount to showing thatthe argument's form can't be valid since it doesn't hold under other interpretations, and thus there mustbe some unstated assumptions in the original.

do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
Do somebody tell me a best nano engineering book for beginners?
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
what is nano technology
what is system testing?
preparation of nanomaterial
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
what is system testing
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
how did you get the value of 2000N.What calculations are needed to arrive at it
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