例设/:E→R记EA={x∈E:f(x)>a则 Lf>al ∪E n=1 ∫≥a+ (=∪E n=11/>0 n (,+∞)=Ua+n,+) (=∪(a+1,+∞)) a a+1例 设f : E → R,记E[ f a] ={x E : f (x)  a},则 [ ] 1 [ ] 1 n f a n E f a E  +  =  =  ( [ a a+1/n ( ( , ) ) 1 1 =  + +  = n n a ( ) [ ] 1 1 n f a n E  +  = =  ( , ) [ , ) 1 1 + =  + +  = n n a a