OK, so for this guy, domain of definition, which is plane minus the origin with the origin removed is not simply connected.

好滴，目前这里，在有定义的区域里，减掉原点，即移去原点，就不是单连通的。

youdao

Parallel lines are, by definition, lines on the same plane that never join.

按照定义，平行线是在同一平面上永不相交的线。

youdao

The definition of plane central curve with positive integer degree was proposed.

给出了平面正整数次中心曲线的定义和中心命题。

youdao

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