if and only if

基本解释

To see this yourself, design a small test program that will compile if and only if the desired condition is true.
为了能切身体会，您可以设计一个小测试程序，这个程序当且仅当期望的条件得到满足时才可以编译。
Eye of newt goes into the little black bag, if and only if there isreproducible scientific evidence that it works.
把蝾螈眼放入黑色的小袋子，当且仅当有重复性的科学证据表明它的实用性）。
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.
不管什么时候你听到了如果，那么，和，或者，不，如果和只有当，这些逻辑词的时候，所有，是，很可爱的逻辑词，你这周要很敏感，因为我想听到你们。

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.
如果你纯洁，不只是肉和食物，肉和酒会变得纯洁，所有的只是，无论善恶都会变得纯洁。
耶鲁公开课 - 弥尔顿课程节选
It's as if the commodity of the bride is deemed truly valuable only if it can be guaranteed pure and untouched.
这就好像新娘这件商品,只有在完全的纯净没有动过才是有真正价值的。
耶鲁公开课 - 弥尔顿课程节选

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

当且仅当
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.
本文证明了：图G是二部图当且仅当其邻接矩阵A（G）的任一个奇阶主子阵是奇异阵。
计算机科学技术
若且唯若