设E为R中可测集,证明D(E)={(x,y):x-y∈E}为R2中可测
问题描述：
设E为R中可测集,证明D(E)={(x,y):x-y∈E}为R2中可测
答
Define f:R^2 -->R,(x,y) |------> x-y.
f is continuous,hence measurable.
It implies that D(E) = f^(-1)(E) is measurable in R^2.