

Of course you can say it, it's just a vacuous truth, and exactly equivalent to saying "there is no element in the empty set that isn't a prime number", no trouble there
It's just the second case described here: http://en.wikipedia.org/wiki/Vacuous_truth[^]
What you can't say is "there exists an element x in the empty set such that P(x) is true"





Forget my last posting it is trash. I didn't know what I wrote.
Yes, I know what vacuous truth is. And I don't want to raise to question.
harold aptroot wrote: clearly an empty set contains only prime numbers
That is wrong, because:
any set X, the empty set 0 is a subset of X. This is equivalent to asserting that every element of 0 is an element of X, which is vacuously true since there are no elements of 0.
(from your link).
That doesn't mean it contains only prime numbers. That means that the empty set is part of prime numbers (as it's part of every other set), by meaning of vacuous truth.

Author of Primary ROleplaying SysTem
How do I take my coffee? Black as midnight on a moonless night.
War doesn't determine who's right. War determines who's left.





ihoecken wrote: That means that the empty set is part of prime numbers (as it's part of every other set), by meaning of vacuous truth. Ok, obviously
ihoecken wrote: That doesn't mean it contains only prime numbers. Why not?





Here is another true funny one: "The set of nonprimes does not contain only prime numbers"





harold aptroot wrote:
ihoecken wrote: That doesn't mean it contains only prime
numbers. Why not?
I'm no mathematician, but i guess it's because the empty set is also a subset of the set of all prime numbers.
The thing is: as the empty set contains no elements, you can't proof nothing about the type of it's elements.
This is one of the problems the Principia Mathematica had, that led Kurt Gödel to state that mathematica is incomplete.
I'm brazilian and english (well, human languages in general) aren't my best skill, so, sorry by my english. (if you want we can speak in C# or VB.Net =p)





harold aptroot wrote: because the same vacuous truth of "all elements are of type t" is true for all
t.
yes, but that statement only holds true if there is an element. the empty se contains none.
I'm brazilian and english (well, human languages in general) aren't my best skill, so, sorry by my english. (if you want we can speak in C# or VB.Net =p)





It is no more wrong to say that ∀x∈0:x∈T than it is to say that "all Leprechauns are Irish".
There is no claim that ∃x∈0:x∈T ("there exists an Irish leprechaun").
The negation of my claim is that ¬∀x∈0:x∈T ("not all leprechauns are Irish") which would have to be proven by showing that ∃x∈0:x∈T ("there exists a nonIrish leprechaun").
The (minority) mathematical faction of Constructivism holds that proof by negation is invalid; the obvious falsity of the negation is insufficient to proove the proposition. There seem to be more constructivists in this thread than have ever gathered before in one place.
An argument Harold already posed is relevent to address this stance:
The empty set is a proper subset of every other set. If an argument references a typed set, 0 must inherit the type. If it were allowed to not be of the referenced type, it could not have been a subset of the typed set. Harold is correct is typing 0 as exclusively prime...remembering that is can also be exclusively type as nonprime in another argument on another day!
Cheers!
[Sorry to bump so late in the game. I was deadset against Harold and Bob (almost angry with them for their obstinance!) for a full hour of parsing this thread before their arguments convinced me that my intuitive distaste for their proposition was wrong.]





Vijay Sringeri wrote: Why this unique ability for prime numbers ?
Which one exactly ?
Vijay Sringeri wrote: How is it possible that, any number can be expressed as product of prime factors ?
Proof.[^]
Vijay Sringeri wrote: What is it, which makes these prime numbers special ?
As you have pointed out, their properties can be used in a lot of algorithms. But this is the case for other "type" of numbers having other properties used in other type of algorithms. So your question is no easy to answer... It is like asking why knives are useful to cut something.
~RaGE();
I think words like 'destiny' are a way of trying to find order where none exists.  Christian Graus
Do not feed the troll !  Common proverb





Hey Rage,
That was a sharp, and precise reply. Thanks.
The link for "Euclid's lemma" was helpful, however it builds other theorems based on the fundamental fact that " Any non prime number can be expressed as product of prime numbers".
Lastly, what an explanation..
Rage wrote:
As you have pointed out, their properties can be used in a lot of algorithms. But this is the case for other "type" of numbers having other properties used in other type of algorithms. So your question is no easy to answer... It is like asking why knives are useful to cut something.
I just loved it, But sadly.. This is what I want someone to answer for me..





Vijay Sringeri wrote: I just loved it, But sadly.. This is what I want someone to answer for me..
Here you go:
Knives are useful to cut for their sharp edges
To alcohol! The cause of, and solution to, all of life's problems  Homer Simpson

Our heads are round so our thoughts can change direction  Francis Picabia





Vijay Sringeri wrote: The link for "Euclid's lemma" was helpful, however it builds other theorems based on the fundamental fact that " Any non prime number can be expressed as product of prime numbers".
There is nothing in mathematics that is not based on other proofs, assumptions and/or definitions.
And there is a proof for that lemma.






Hey, this is my standard answer to my children's questions.
~RaGE();
I think words like 'destiny' are a way of trying to find order where none exists.  Christian Graus
Do not feed the troll !  Common proverb





Thanks all, for showing keen interest in answering/trying to answer this questions.
But my question still remains unanswered
However, I just wanted to put some info here.
Prime number : Numbers > 1, and which has 1 and itself as it factor is prime nuber.
Composite number : All non prime numbers are composite numbers.
What about 1 then ?
1 is neither prime nor composite.





Wheter or not to include 1 in the list of prime numbers is debated among mathematicians. There are arguments to include it, and argument to not include it.
1 cant be written as a product of smaller primes except 1*1
However 1*N = N so you could always write any nyumber as a product of two primes if that was the case.






Quote: Why this unique ability for prime numbers ?How is it possible that, any number can be expressed as product of prime factors ?
Both of these two questions could be answered by the fundamental theorem of aritmatic.
Quote: What is it, which makes these prime numbers special ?
You could read my article, and there are lots of referances there.
Finding prime numbers[^]





Thanks a lot, your article is very informative.





Vijay Sringeri wrote: Why this unique ability for prime numbers ?
It is not a unique ability for prime numbers, it is just that these numbers can not be subdivided any further. You can find the LCM and HCF using any numbers, but they will always be a combination of prime factorials, so using prime numbers is far easier.
Vijay Sringeri wrote: How is it possible that, any number can be expressed as product of prime factors ?
Essentially because a prime number can not be divided and a non prime number can be.
Any number n that is not prime has at least two divisors that are not 1 and n. These divisors are either prime or non prime. If they are non prime then by definition they follow the same rule as n. These numbers are smaller then n, so repeating this rule will always result in only prime divisors.
Vijay Sringeri wrote: What is it, which makes these prime numbers special ?
The fact that they are prime and can not be divided.





Member 2053006 wrote: Any number n that is not prime has at least two divisors that are not 1 and n.
what about 4 ? AFAIK, for has only one divisor thats not 1 or 4, and it's 2...
I'm brazilian and english (well, human languages in general) aren't my best skill, so, sorry by my english. (if you want we can speak in C# or VB.Net =p)





The complete lack of any mention of Zero in this discussion has sucked out all meaning for me, and left me inside a total vacuum.
Since Zero multiplied, or divided (except of course Zero divided by Zero), by any number, natural perverted, or even fractional, will always be Zero: therefore Zero is the Prime of Primes, not to mention that Zero raised to any power remains Zero, not to mention that subtracting Zero from, or adding Zero to, any number leaves the number unchanged !
That any number divided by Zero is an infinity (whose ordinality, or Aleph, among other possible infinities: is ultimate ?) which cannot be conceptualized within linearly digital Turing/Von Neumann theoretical computational design, and must be expressed by some "placeholder" like "undefined," or "NaN," or will, on a practical level, in many circumstances crash a computer: is proof of its sacred power.
Zero is the unique singularity of the transition between positive and negative numbers, thus equivalent to the Omphalos, the stone of the navel of the geobody of the cosmos, which for the ancient Greeks was located at the shrine of the oracle at Delphi.
I propose to you that the infinite set of all possible prime numbers is contained within the infinity created by Zero divided by Zero like a tiny foot in a huge shoe: lots of wiggleroom no matter what #1 does, or does not, do.
best, Bill
"Takuan Sōhō died in Edo (presentday Tokyo) in December of 1645. At the moment before his death, Takuan painted the Chinese character 'meng' ("dream"), laid down his brush and died."





BillWoodruff wrote: That any number divided by Zero is an infinity
Normal mathematics defines that as undefined, not infinity.
A divisor that approaches an infinitely small value produces a value that approaches infinity.





I think he was talking about Lim(1/0), that is infinity.
for any other operation, 1/0 is undefined, just because no one can think what would be the result.
I'm brazilian and english (well, human languages in general) aren't my best skill, so, sorry by my english. (if you want we can speak in C# or VB.Net =p)





Limit(lim) is still a convergence sequence. Which is the same as what I said.
And equating it to infinity is a misrepresentation of what it means mathematically.





yes, you are right, i couldn't remember of the correct simbol to use, so i used equals, as that was what my mathematical analysis (that's how it's called in my universsity) used.
I'm brazilian and english (well, human languages in general) aren't my best skill, so, sorry by my english. (if you want we can speak in C# or VB.Net =p)





Because the "secret" factors A*B = C, with A prime and B prime, are the holy grail to break RSA, the asymmetric keys algorithm used world while to enforce security, with SSL, HTTPS, VPNs...
Ruffly speaking, in RSA itself, C is "the public key" and its factorization, A and B "the private key".
It is straightforward to find the factors for small numbers, but it happens that it is very hard to find such factors for large numbers (indeed  you need to extensively search for them).
To date it has been possible to break up to a 768 bit RSA key (C is 768 bits long) by using a cluster of many hundred servers. Larger keys (1024, 2048 bits) are still considered secure (needed hundred years of cluster computing time for one single key)  and they will, until some strong improvement will be performed in number theory.





+5 for a Computer Science answer.
I'm brazilian and english (well, human languages in general) aren't my best skill, so, sorry by my english. (if you want we can speak in C# or VB.Net =p)





Mathematicians love to decompose things. The parts of a thing a usually easier to handle.
When they considered the integers and the law of addition, they saw nothing interesting. Any integer larger than 2 decomposes into smaller parts: 12 decomposes into 1+11, 2+10, 3+9, 4+8, 5+7 and 6+6. This is trivial. 1 cannot be decomposed, so 1 is the only "prime" as regards addition.
When they considered the integers and the law of multiplication, things got funnier: 12 decomposes into 2 x 6 and 3 x 4, 6 decomposes into 2 x 3 and 4 decomposes into 2 x 2. But 2 and 3 cannot be decomposed.
So the idea of primes came quite naturally by discovering thoses numbers that cannot be decomposed. And they found much less regularity, meaning cool things to study.
There is no real mystery in the decomposition: either a number cannot be decomposed, then it is called prime, or it can be decomposed, then it is called composite. You can apply the same reasoning to its parts, which are smaller. In the end, you always end up with prime factors, because decomposition is a finite process. (This is a case of infinite descent[^].)
More mysterious is the fact that the decomposition is unique: whatever the way you apply the decomposition, you always end up with the same factors with the same multiplicity. Example: 12 = 2 x 6 = 2 x 2 x 3 or 12 = 3 x 4 = 3 x 2 x 2. But you easily understand that if a prime factor p appears r times in one decomposition of an integer n and s times in another (let r < s), we have a problem, as if we divide n by p^s, in the first case we will get a nonzero remainder and in the other case a zero remainder !
What makes prime numbers so attractive is that mathematicians have failed so far to find simple structures in their distribution, leading to the famous Rieman's hypothesis[^], considered a major unsolved problem in modern mathematics.





What is your question? The definition of primes is that they cannot be divided (within the set of whole numbers) by any other whole number other than 1 or the number itself. Everything else you write is an immediate consequence of that definition.
Ok, a bit more in detail:
 Any nonprime can be expressed as product of prime factors.
With the correction, this is really an immediate consequence and occasionally used as an alternate definition of what is a prime (as in: any number not expressable in that way is a prime)
 Prime factors can be used to check whether a number divides "N" ( N  Integer )
Lets say that N=n1*n2*n3, where n1, n2, n3 are the prime factors of N. If a number M is divisible by N, then there is some integer K, so that
K=M/N
or:
K=M/(n1*n2*n3)
Now multiply both sides with (n2*n3), and you get
K*n2*n3 = M/n1
As you can see there is an integer K1=K*n2*n3 for which K1=M/n1 , and therefore n1 is a divisor of M. The same is true for n2 and n3  both are divisors of M. Now that you know that if N is a divisor of N, then its prime factors are also divisors, you can turn that knowledge around: You test whether M is divisable by n1! If you find out that M is not divisible by n1, it means that it cannot be divisible by N either!
 Prime factors can be used to find LCM and HCF
Given two numbers N and M, you may express them as a product of prime factors N=n1*n2*...*nk and M=m1*m2*...*ml. (if N or M is a prime, there will only be one number n1 or m1 respectively. But that doesn't stop the following conclusion) HCF is the product of the factors you get from intersecting the two sets of prime factors. If you multiply that number by anything else, it will either no longer be a divisor of N, or of M.
LCM is pretty similar, but I'm running out of time at this point In any case, this property follows from the definition as well.





Vijay Sringeri wrote: Why this unique ability for prime numbers ?
Because God made it so.
Vijay Sringeri wrote: How is it possible that, any number can be expressed as product of prime factors ?
Because the big bang for this universe of all the multiverses made it so.
Vijay Sringeri wrote: What is it, which makes these prime numbers special ?
Gaea is the answer.
Vijay Sringeri wrote: Can someone explain me this mystery behind prime numbers
Classic logic.
All of mathematics and many of the theoretical parts of sciences are based on proofs, assumptions and/or definitions. There is nothing else.
You can look to basic philosophy for the answer but it will not provide one. But it might provide a better understanding of why there is no answer.





Vijay Sringeri wrote: What is it, which makes these prime numbers special ? A prime number is one that can't be divided by any other number other than itself or 1. I learned 1 was a prime, but excluded from the rules defining additional prime numbers because if it wasn't, there would only be one prime number: 1.
The definition of a prime number makes it special.
Vijay Sringeri wrote: How is it possible that, any number can be expressed as product of prime factors?
One of the prime factors is 1. 1*3 is 3. ALL prime numbers can be multiplied by 1, therefore they are a product of prime factors. The rest of the numbers are products of prime numbers. (That you can then multiply 10 billion times by 1 if you want.)
Actually, not any number is a product, any INTEGER number is a product of primes. You can never get 3.14157 as a product of primes. I take it back, ONLY positive numbers can be derived from prime products. 0 is not a prime, nor is 1. You can forget about immaginary numbers too. In the lexicon of numbering systems, primes are really limited.Vijay Sringeri wrote: Why this unique ability for prime numbers ? It's defined this way. (These statements also implies all the restrictions I mentioned.)





Pfft[^]
c.f. 3.8l eType[^], which presumably didn't need plugging into a windmill after it performed its run.
electric car = slow, boring and not cool.
eType = fast [for its day] exciting and way cool.
In their defence, I suppose, they did just hotrod a milk float.





If only there was a new etype[^] ...
Panic, Chaos, Destruction. My work here is done.
Drink. Get drunk. Fall over  P O'H
OK, I will win to day or my name isn't Ethel Crudacre!  DD Ethel Crudacre
I cannot live by bread alone. Bacon and ketchup are needed as well.  Trollslayer
Have a bit more patience with newbies. Of course some of them act dumb  they're often *students*, for heaven's sake  Terry Pratchett






I saw this beauty[^] near work recently (obviously not this week!)
====================================
Transvestites  Roberts in Disguise!
====================================





Shame she's partly hidden by the car.





This is Wilmslow  she's probably in her eighties!
====================================
Transvestites  Roberts in Disguise!
====================================





To quote Paul Calf, you're just getting fussy now.






Ok, so it did 148mph. How long could it do it for? Enough to go down the shops? Get to work and back? Last a month on a "full tank"? Somehow I doubt it.
Ideological Purity is no substitute for being able to stick your thumb down a pipe to stop the water





Yeah, but who wants to deal with SU carbies? Pain in the bum.
cheers,
Chris Maunder
The Code Project  Cofounder
Microsoft C++ MVP





Unless I'm missing something in one of the articles...
E Type top speed: 149.1 mph
Nemesis top speed: 151.6 mph
151.6 > 149.1





According to the first troubleshooting tip in this lovely Exception [^], I may have been trying to cast a number greater than infinity. I'v gots skillz.
There are only 10 types of people in the world, those who understand binary and those who don't.





ryanb31 wrote: greater than infinity Nope, it says "must be less than infinity", not "must be less than or equal to infinity".





Details, schmetails. Why should ryan's selfelevation be stopped by flimsy facts?





But equal to infinity doesn't always make sense, two different infinities may be unequal.





Sure, but you still can't rewrite "not less than infinity" to "more than infinity"





My point is that inequalities involving infinities don't always act as expected to begin with (e.g. ∞ < ∞ can be true), so applying the usual rules doesn't always work. But you are correct.






Chuck Norris could have actually pulled it off  if it wasn't for the fact that when Chuck Norris assigns a value to a numeric variable, it wouldn't THINK of overflowing...
".45 ACP  because shooting twice is just silly"  JSOP, 2010  You can never have too much ammo  unless you're swimming, or on fire.  JSOP, 2010  "Why don't you tie a kerosenesoaked rag around your ankles so the ants won't climb up and eat your candy ass."  Dale Earnhardt, 1997



