if

no, iff.
its an abbreviation for "if and only if"
http://en.wikipedia.org/wiki/If_and_only_if

I see. Thank you.

you're welcome. I admit I was waiting for that comment ;).

haha great, did you tag it "useful info" =D ?

I did. But who on earth tagged it as controversial?

(someone who has found a way to enter the imaginary domain, I suppose)

No, I did, because the natural numbers are often defined to NOT include 0 :P.

And so we enter the math department...

Doesn't one usually speak of "greater" rather than "superior" in mathematics? I don't think I've ever seen it phrased like this.

you're probably right, thx.

That's why I added the second translation, actually.

I was going to say that this was probably something from the French, but "superior to" is still very valid, IMO, even in English. More erudite books might use it. But yes, the more common natural thing would be "greater than".

I'd like to go back to this "iff"

Is it really possible to use this "word" in a sentence like this one?

I believe it's just a short form of "if and only if" in logical formulas, for example you certainly might write: "For any p, q, and r: (p & q) & r iff p & (q & r)", but it's not a real sentence.

Could you really "iff" in a normal sentence, like in the definition of a natural integer? Maybe you still have to write "An integer is natural if and only if it is greater or equal to 0"?

I think it is used in what you call "normal" sentences.
For example in the Wikipedia article, there are examples for it:
http://en.wikipedia.org/wiki/If_and_only_if

I would rather write that an integer is a natural number, than that an integer is natural. I do not think that "natural integer" is a thing.

Not a native English speaker, but I am a research mathematician with international collaborations in English.

I do not remember anyone saying "iff", and furthermore, it is very easy to confuse with a pronounced "if" and the distinction is crucial, so I would recommend pronouncing "iff" as "if and only if".

I can not comment on native English mathematicians speaking with each other.

I would say that writing "iff" is more of a shorthand notation or casual writing. I do not recall ever seeing it in formal mathematical writing (published articles or textbooks). I could imagine it as a part of lecture or slides, but still, it would be a potential source of confusion even there.

It should probably be read "if and only if", and it should probably be spelt out like that as well.

The shorthand "iff" is certainly used in more casual contexts. I do not think it is a good idea in general, but it is used.

I searched Arxiv, a repository with many mathematics (and physics and computer science) preprints, and there were a few instances of the abbreviation in serious articles, so it does seem to happen: https://duckduckgo.com/?q=iff+site%3Aarxiv.org

I would still expand it when pronouncing.

Duplicates of this sentence have been deleted:
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