# If and only if



## RaLo18

If and only if, or iff, is used to describe a relation between two statement, mainly in logic, but also in math or related fields.
The most known example of iff in math is the Pythagorean theorem: a triangle is right iff its perpendiculars, a and b, and its hypotenuse, c, fulfill a^2+b^2=c^2.

How do you say 'if and only if' in your language?

Hebrew:
אם ורק אם (_'im verak 'im_) or אםם (similar to iff).


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## Agró

In *Spanish*: ...si, y sólo si, ...


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## szal

Interesting, never heard of ‘iff’...

In German, in mathematical contexts, it’s “genau dann, wenn” (literally: “exactly then, when/if”).


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## Erick404

In Portuguese, the structure is the same as Spanish and English:
_Se, e somente se, ..._


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## apmoy70

In Greek it has the same structure:
Αν και μόνον αν
an ke m*o*non an
if and only if
In Mathematics, «Αν και μόνον αν» is written «αν-ν» ("an-n")


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## Mauricet

Le théorème de Pythagore : _Un triangle ABC a un angle droit en A *si et seulement si* AB^2 + AC^2 = BC^2._


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## Volcano

*In Turkish

Ancak ve ancak*


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## sakvaka

Finnish: _jos ja vain jos_ or _joss_.
The latter is used in mathematical and logical contexts only.

_Pythagoraan teoreema: Kolmio on suorakulmainen, jos ja vain jos sen hypotenuusan neliö on yhtä suuri kuin kateettien neliöiden summa._


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## Outsider

Erick404 said:


> In Portuguese, the structure is the same as Spanish and English:
> _Se, e somente se, ..._


Also *se e só se*, abbreviated to "*sse.*"


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## Hutschi

szal said:


> Interesting, never heard of ‘iff’...
> 
> In German, in mathematical contexts, it’s “genau dann, wenn” (literally: “exactly then, when/if”).


 
Additionally there is an additional expression:

"Dann, und nur dann, wenn ..."

(Than and only than/then and only then, if).

I have the feeling that this is more often used outside of mathematical proofs. The meaning is the same.


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## Awwal12

> Additionally there is an additional expression:
> "Dann, und nur dann, wenn ..."
> (Than and only than/then and only then, if).


Almost exactly as in Russian ("togd*a*, i t*o*l'ko togd*a*... kogd*a*"; literally "in case/time and only in case/time, if/when"): 
Typical syntax:
_Object_ "тогда, и только тогда" _Statement_, "когда" _Condition._

Also mathematicians use a special term "необходимое и достаточное условие" ("neobkhod*i*moye i dost*a*tochnoye usl*o*viye") - "indispensable and sufficient condition". Then they usually describe this condition. ))


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## Outsider

Awwal12 said:


> Also mathematicians use a special term "необходимое и достаточное условие" ("neobkhod*i*moye i dost*a*tochnoye usl*o*viye") - "indispensable and sufficient condition".


A necessary and sufficient condition. But that's a somewhat different expression.


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## Awwal12

Outsider said:


> A necessary and sufficient condition. But that's a somewhat different expression.


Surely, but it looks like to be used more frequently, at least in high mathematics.


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## Hutschi

German: "Genau dann" und "dann und nur dann" drücken eine notwendige und (zugleich) hinreichende Bedingung aus.

"Genau dann" and "dann und nur dann" express a necessary and (at the same time) sufficient condition.


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## Frank06

Hi,

In *Dutch (Flanders)* the standard phrase in the context of logic would be: _als en slechts als_. 
According to Wikipedia, which does have a page about it in various languages, in the *Netherlands* the phrase "_dan en slechts dan als_" is common.

Groetjes,

Frank


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## federicoft

Italian: _se e solo se_.


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## Encolpius

*Hungarian*: _akkor és csakis akkor_


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## phosphore

French: ssi (si et seulement si)

Serbian: akko (ako i samo ako)


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## Orlin

Awwal12 said:


> Almost exactly as in Russian ("togd*a*, i t*o*l'ko togd*a*... kogd*a*"; literally "in case/time and only in case/time, if/when"):
> Typical syntax:
> _Object_ "тогда, и только тогда" _Statement_, "когда" _Condition._
> 
> Also mathematicians use a special term "необходимое и достаточное условие" ("neobkhod*i*moye i dost*a*tochnoye usl*o*viye") - "indispensable and sufficient condition". Then they usually describe this condition. ))


 
Bulgarian is quite the same: the commonest expression is тогава и само тогава, когато ...., the other possibilities are в този и само този случай and the literary translation ако и само ако (I think that the last is very rare). Mathematicians also use the term необходимо и достатъчно условие.


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## hollabooiers

In *Estonian* it's either _siis ja ainult siis, kui_ or _parajasti siis, kui__. _I've seen both used, but I think _parajasti siis, kui _might be somewhat more uh.. popular.


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## Dymn

Agró said:


> In *Spanish*: ...si, y sólo si, ...


In Spanish, or Catalan for that matter, the abbrevation _sii _is also used. I've also read _ssi_, but it strikes me as less common.


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## nimak

*Macedonian*

Same structure as in English:
If and only if = Ако и само ако (Ako i samo ako)

In Mathematics it is shortened as акко (akko) = iff


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## bibax

Czech (similarly like in Russian "тогда, и только тогда"):

*tehdy a jen tehdy* (no abbreviation similar to iff, ssi, akko, ...)

in other words it is an equivalence:

a triangle is right <=> a^2+b^2=c^2


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