试证明: 设,则E可测的充分必要条件是:对任给ε>0,存在开集G1,G2:,,使得m(G1∩G2)<ε.
试证明:
设,则E可测的充分必要条件是:对任给ε>0,存在开集G1,G2:,,使得m(G1∩G2)<ε.
m(G1\E)<ε/2,m(E\F)<ε/2,
m(G1\F)≤m(G1\E)+m(E\F)<ε.
令G2=Fc,易知G2是开集且有,我们有m(G1∩G2)<ε.
充分性 假定存在,,使得m(G1∩C2)<ε,则令,易知,且有m(G1\F)<ε.从而可知m*(G1\E)<ε,即E是可测集.