定义:设 (X,T)——拓扑空间,F 是 X 的一个开覆盖. 若 F' F, 且 F' 也是 X 的覆盖,则称 F' 为 F 的子覆盖. 若 F' 是有限集族,则 F' 是有限子覆盖. 定义:,若拓扑空间 (X,T) 的每一个开覆盖有限的子覆盖,则 称(X,T) 为 紧致 (拓扑)空间. 题目:以下那些关于 (R,T5)的话是真的?
【简答题】选择所给词或短语并用其正确形式填空 coffee, exercise, better, healthy, sleep ...but I’m pretty healthy. I __小题1:__ every day, usually when I come home from school. My eating habits are pretty goo...
【简答题】阅读理解 You are what you eat Keeping better eating habits can help you reduce (减少) disease. A healthy eating plan means choosing the right foods to eat and preparing foods in a healthy way. _____________...