双面均凹进的；双凹的。

Concave on both surfaces; biconcave.

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一根两端有把手的绳抖动一个底面圆形、侧面双凹的木质物体转动或抛起。现在，有很多人在公园里玩这个传统的体育项目。

The Chinese yo-yo is a sport from China consisting of two equally-sized discs connected with a long axle. Nowadays, this traditional sports that many people play it in the park.

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在本文中，我们提出了双凹规划问题和更一般的广义凹规划问题。

In this paper, we put forward biconcave programming problem and generalized concave programming problem more generally.

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