本文引入直投射覆盖的概念，证明了环R为左完全环当且仅当每一个左R-模（平坦左R-模）具有直投射覆盖；

This peper introduces the concept of direct-projective covers, and prove that a ring R is left perfect if and only if every left R-module(flat left R-module) has a direct-projective cover;

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当然，那将是小丑，一个恶魔般的三环马戏团人物，被希斯·莱杰完全地发挥出来。

That would be the Joker, of course, a demonic creation and the three-ring circus of one wholly inhabited by Heath Ledger.

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这一环境的配置应该与产品环境的配置完全相同。

This environment should be set up identical to the production environment.

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