| 2. | Fairly important covers have point - countable bases , weakly bases , k - networks , sequence - neighbourhood networks and so on . fairly important mappings have quotient s - mappings , closed s - mappings , open mappings , open - and - closed mappings , com - pact - and - open mappings , perfect mappings , countable bi - quotient mappings , compact mappings 比较重要的覆盖有点可数基,弱基, k网,序列邻域网;比较重要的映射有商s映射,闭s映射,开映射,开闭映射,紧开映射,完备映射,可数双商映射,紧映射。 |