if and only if

基本解釋

To see this yourself, design a small test program that will compile if and only if the desired condition is true.
為了能切身體會，您可以設計一個小測試程序，這個程序當且僅當期望的條件得到滿足時才可以編譯。
Eye of newt goes into the little black bag, if and only if there isreproducible scientific evidence that it works.
把蠑螈眼放入黑色的小袋子，當且僅當有重復性的科學證據(jù)表明它的實用性）。
Whenever you hear the word If, then, and, or, not, If and only if, all these logical words, all, is, lovely logical words, you've got to be sensitized this week because I want to hear you.
不管什么時候你聽到了如果，那么，和，或者，不，如果和只有當，這些邏輯詞的時候，所有，是，很可愛的邏輯詞，你這周要很敏感，因為我想聽到你們。

If you start a path of one color you must continue to use only toe and handholds marked with that color.
If you're pure, not only are meats and viands pure , but all kinds of knowledge, whether of good and evil.
如果你純潔，不只是肉和食物，肉和酒會變得純潔，所有的只是，無論善惡都會變得純潔。
耶魯公開課 - 彌爾頓課程節(jié)選
It's as if the commodity of the bride is deemed truly valuable only if it can be guaranteed pure and untouched.
這就好像新娘這件商品,只有在完全的純凈沒有動過才是有真正價值的。
耶魯公開課 - 彌爾頓課程節(jié)選

From an evolutionary viewpoint, a function can be assigned to a DNA sequence if and only if it is possible to destroy it.
FORBES: ENCODE Papers Get A Fisking

當且僅當
It is proved that a graph G is a bipartite graph if and only if every odd-order princpal minor of the adjacecy matrix A (G) of G is singular.
本文證明了：圖G是二部圖當且僅當其鄰接矩陣A（G）的任一個奇階主子陣是奇異陣。
計算機科學技術
若且唯若