Let $U\subset\mathbb R^m, V\subset\mathbb R^n$ be open sets and $f:U\times V\to \mathbb R$ a continuous function. I want to prove
$$\int_Udx\int_Vf(x,y)dy=\int_Vdy\int_Uf(x,y)dx=\int_{U\times V}f$$
If the integral $\int_{U\times V}f$ is convergent.
This is a kind of a generalization of the repeated integral theorem which uses blocks instead of open sets (these open sets can be bounded or unbounded).
If these open sets are bounded we cover these ones with blocks and apply the repeated integral theorem. I don't know how to proceed if these open sets are unbounded.