当且仅当

Furthermore, it is shown that every pure projective left R-module is closed under pure submodule if and only if every pure injective left R-module is closed under pure epimorphic image.

最后，作为应用，证明了每一纯投射左R-模在纯子模下封闭当且仅当每一纯内射左R-模在纯满像下封闭。

It is proved that a left R-module P is pure projective if and only if for any pure epimorphism E→M→0, where E is pure injective, Hom→Hom→0 is exact.

证明了左R-模P是纯投射的当且仅当对任意纯满射E→M→0，其中E是纯内射的，Hom→Hom→0是正合的。

In 1986,in the paper [1] Junnila proved the result :A space is hereditarily metacompact iff its every scattered partion has a point finite open expansion .

Junnila在文[1]中证明了：一个空间是遗传亚紧的当且仅当它的每个散射分解有一个点有限的开膨胀。

Firstly, it's proved that the base of free monoid is unique, and that the equation of a base, a generating set and a irreducible generating set in the semigroup with length; Secondly, it's given the relation of a primitive word and a word of indecomposable--Let and is indecomposable, then is primitive ;And by using the length's method and chart,some properties of primitive word have been proved and the solutions of the equation , are discussed; Lastly, on the base of some proposition in Free monoids and Languages ,the proofs of some properties are improved by instruction. For example: Let be a primitive word over X, where .Then is a code. And let then if and only if {} is a code.

首先，讨论了含幺半群中基的基本性质及基与最小生成元集的联系，并给出了含幺半群中基、生成元集、不可约生成元集三者之间的关系；证明了在有唯一长度的半群S中，不可约生成元集、基、最小生成元集三者之间的等价关系；其次，讨论了字的组合与分解性，得出了字的本原性与不可分解性之间的关系---若为不可分解的，则一定是本原的，反之，不一定真；并运用图示法证明了字的可补性理论，讨论了方程，的可解性；在此基础上，用归纳法进一步证明了本原字与码的有关命题--若是X上的一个本原字，其中，则是一个码；若则当且仅当{}是一个码。

Furthermore, it has been proved that gis standard if and only if any integrable highest weight module of g is irreducible.

证明了g是典范的当且仅当g的任一可积最高权模不可约(定理2.3)。

It is proved that a wrpp semigroup satisfies a permutation identity if and only if it satisfies the identity xyzw= xzyw.

证明了wrpp半群满足置换恒等式当且仅当它满足恒等式xyzw=xzyw。

You can achieve anything you desire IF and only IF, what you desire is part of life's greater plan for you.

您可以实现任何你希望的当且仅当，你的愿望是生活的一部分的更大计划的你。

We present an analysis of the defect by inverse Fourier transformation.

结果发现，当且仅当反映面心有序的超结构反射被用来作反Fourier变换时，晶格条纹在反相畴界处错开。

Eliminating the restriction of the characteristic of field ,the forms of invertible linear operator preserving inverses of matrices over full matrix space with at least four elements are described.

去掉了域的特征限制，刻画了至少包含4个元素的任意域 F上的全矩阵空间Mn的保逆的可逆线性算子形式。利用保幂等的结论证明了f为Mn上保持逆矩阵的可逆线性算子当且仅当存在P∈GLn，使得f=εPAP-1，A∈Mn，ε=±1∈F；或者存在P∈GLn，使得f=εPATP-1，A∈Mn，ε=±1∈F

In chapter 2, we prove that an abundant semigroup satisfying the regularity is a locally E-solid semigroup if and only if it is an E-local isomorphic image of some abundant Rees matrix semigroup AM over an E-solid abundant semigroup with entries of the sandwich matrix P being regular elements of T.

第二章，我们证明了满足正则性条件的富足半群是局部E-solid(quasi-adequate，R~*-unipotent)半群当且仅当它是某个富足Rees矩阵半群RM的E-local同构像，其中sandwich矩阵的P元素是T中的正则元。

However, as the name（read－only memory）implies, CD disks cannot be written onorchanged in any way.

然而，正如其名字所指出的那样，CD盘不能写，也不能用任何方式改变其内容。

Galvanizes steel pallet is mainly export which suits standard packing of European Union, the North America. galvanizes steel pallet is suitable to heavy rack. Pallet surface can design plate type, corrugated and the gap form, satisfies the different requirements.

镀锌钢托盘多用于出口，替代木托盘，免薰蒸，符合欧盟、北美各国对出口货物包装材料的法令要求；喷涂钢托盘适用于重载上货架之用，托盘表面根据需要制作成平板状、波纹状及间隔形式，满足不同的使用要求。