In the English language, there is a phrase "if and only if"

The last snow 🌨 ❄ of late winter in the state of Colorado (the red state) shall kill vegetable seedlings 🌱 if and only if fewer than 8 lunar cycles have passed since the first snow of fall or early winter.

What is a simplified manderin phrase for "if and only if" in this context involving snow killing edible plants.

Example of multiples of ten

for any number x

x is a multiple of ten

if and only if x is a multiple of 5 and the number is a multiple of 2).

What is the manderine phrase for if and only if in the context of numbers?

Example of a car in the middle of an intersection

for each car or automobile x

Car x is located where two or more roads cross, collide, or intersect.

if and only if only if there is number n ≥ 3 and
there are two decimal numbers d1 and d3 such that. for any decimal number d2
if 0 < d1 < d2 < d3 then for any circle with radius d2

there are n segments of this circle lying on a road.

An Example that speaks of slow-made, quality work

For example, if you do quality work, you work very slowly. However, if you work very slowly, it does not mean that you will produce quality work.

It is false that, for any type of work, x, x is quality work if and only if x is slow work.

For example, I know how to paint a house very slowly and do a bad job. I do not know how to do good quality painting, but if I knew how to do a good quality paint job on a house, then it would take me a long time to paint that house.

What was the question?

What is the simplified chinese expression for "if and only if" or .ay e the word "equivilantly?

3 Answers 3



当且仅当(英语:if and only if,iff),在数字逻辑中,逻辑算符反异或闸(英语:Exclusive NOR)是对两个运算元的一种逻辑分析类型,符号为XNOR或ENOR或 ⇔ 。

  • 若且唯若 could be a better translation May 7, 2023 at 4:00
  • @envs_h_gang_5 I think they are the same, just preference. I do think yours is more casual, if a technical term can be.
    – zagrycha
    May 7, 2023 at 4:38
  • 3
    若且唯若 looks to be the Taiwanse Guoyu「國語」preferred variant.
    – Mou某
    May 7, 2023 at 11:35
  • This is the official translation used in P.R.C. academia.
    – charlesz
    May 8, 2023 at 20:37

A direct translation of "if and only if" is "如果,只有如果", which doesn't express the intended meaning well in Chinese, at least it is not a common way we speak.

The function of "only" in this phrase is to stress the word 如果 (the important thing has to be said twice)

The better interpretation of "if and only if" is "如果,我说如果" (If, I said if")

  • 如果,我说'如果' X = Y

  • If, I said 'if' X = Y

  • (only when X = Y, the following statement would be valid)

  • "If and only if" is a specialised term in mathematics. In particular, "only if" is the statement B implies A when the if statement is A implies B. It doesn't have the literal meaning of the words.
    – Toby Mak
    May 7, 2023 at 13:03
  • This answer is wrong.
    – charlesz
    May 8, 2023 at 20:37

You can use “当且仅当”:当且仅当A成立,B成立。

Or you can say: B成立的充要条件是A成立。

The expressions above is widely used in textbooks in PRC.


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