My question is really simple. I'm reading a book which states this theorem:
If $f:A_1\times A_2\to \mathbb R$ is integrable and $f$ is continuous then
$$\int_{A_1\times A_2}f(x,y)dxdy=\int_{A_1}dx\bigg(\int_{A_2}f(x,y)dy\bigg)=\int_{A_2}dy\bigg(\int_{A_1}f(x,y)dx\bigg)$$
Is this Fubini's theorem?