Ľ open set and close set
ʬդϡǤդ a Фơš0 ¸ߤ(a,)դȤʤȤ(open set)Ȥ
ʬƤ佸礬λĽ(close set)Ȥ
γΤν² u ȤȰʲΩ롣
- (i)\(,\emptyset \in u\)
- (ii)\(_{1},_{2} \in \cal U \Rightarrow _{1} \cap _{2} \in \cal U\)
- (iii)\(\{_{\lambda};\lambda \in \Lambda\}Ǥդγ²Ȥȡ\bigcup_{\lambda \in \Lambda}_{\lambda} \in \cal U\)
Ȱ topology and topological space
ʬ² \(\cal U\) \(\cal U\) ΰ(topology)Ȥ
ޤ\((,\cal U)\) (topological space)Ȥ