设EnE,fn(x)=χE(x),其中对任意A, 证明
{fn(x)}在E上一致收敛于f(x)的充要条件是: 存在N,对任意n≥N,E[|fn-f|>0]=
min{fn(x),gn(x)}min{f(x),g(x)};
max{fn(x),gn(x)}max{f(x),g(x)}
fn(x)+gn(x)f(x)g(x)