该文利用双g-函数和半连续函数给出了双层空间的刻画,得到:空间(X,Υ1,Υ2)是双层当且仅当对于每一个f∈Υ_i-LSC(X),都对应一个h(f)∈Υi-LSC(X)∩Υj-USC(X)使得(1)0≤h(f)≤f且当f(x)〉0时,0〈h(f)(x)〈f(x).(2)当f≤f′时,h(f)≤h(f′).
In this paper,we give some characterizations of pairwise stratifiable spaces bymeans of pairwise g-functions and semi-continuous functions.It is established that:a space(X,τ1,τ2) is pairwise stratifiable if and only if for each f∈τi-LSC(X),one assigns anh(f)∈τi-LSC(X)∩τj- USC(X) such that(1) 0≤h(f)≤f and 0h(f)(x)f(x) whenever f(x)0.(2) h(f)≤h(f′) whenever f≤f'.