A new method of water quality assessment σ index was given in the present paper.
给出水质评价中的一种新方法σ指数
It is well known that f(F) forms a sigma-algebra over S if f satisfies the bijective condition.
周知,若f满足双射条件,则f(F)构成S上的一个σ-代数。
It is shown that the ideal-mappings are more general than the bijective mappings,and moreover their actions on a set class and the operations of generating a sigma-algebra,a monotone class and a λ-class are commutative.
在可测空间上引进了理想映射的概念,证明了理想映射是比双射更一般的一类映射,同时理想映射在一个集类上的作用与相应的生成σ-代数、生成单调类及生成λ-类运算均可交换次序。