座位

At last, the isochronous center of infinity of a class of quintic systems is studied and all conditions of center and isochronous center are obtained for infinity of this system, which is the first time for the research on the isochronous center of infinity.

最后，研究了一类实平面五次系统的无穷远点的等时中心，给出了系统无穷远点为中心和等时中心的全部条件。这是迄今对无穷远点等时中心进行的首次研究。

To provide or protect with a visor ....

有一个圆形平顶和帽舌的帽子。