多边

A group of projective invariants was derived based on the cross ratio of five coplanar points, and used to recognize planar polygons. Experimental results show that the invariants have projective invariance and can be used to recognize planar polygons effectively.

利用共面五点的交比，导出一组用于识别平面多边形的射影不变量，用这组不变量实现平面多边形的识别，实验结果表明，这组不变量具有射影不变性，可以有效地识别平面多边形。

Guterres says he fully agrees that all countries should practice genuine multilateralism on the basis of the UN Charter and international law, adding that China is vital to the international multilateral system.

古特雷斯表示，他完全赞同所有国家应在《联合国宪章》和国际法的基础上奉行真正的多边主义，并表示中国对国际多边体系至关重要。

Setting up free trade area is important for trade liberalization of ASEAN to avoid difficulties of multi-agreements and drawbacks of multi-trade-system of WTO.

建立自由贸易区是东盟贸易自由化的一个重要层面，以绕开WTO多边协议的困难，克服WTO多边贸易体系的种种弊端。