Solution
= Solution
The <monotone convergence theorem> states that for measurable functions $0\leq f_1\leq f_2\leq\cdots$ converging pointwise to $f$, the limit is measurable and
$$
\boxed{\int f\,d\mu=\lim_{n\to\infty}\int f_n\,d\mu.}
$$
Both sides may be infinite. Monotonicity and nonnegativity replace any need for an integrable dominating function.