In this short paper, we firstly give a short proof of Birkhoff-Kakutani Theorem by Moore metrizable Theorem. Then we pro......

结合拓扑空间的特性讨论函数上（下）极限,得到了一些与实直线上几乎一致的结果。首先给出了拓扑空间中函数上（下）极限的定义。然后证明......