I coudnt have solved this problem, I hope you can give me some idea.
Let a measurable set and , .
Prove that .
1- If E has finite measure apply the inequality above for the set on which f>1 and apply dominated convergence, and on the set on which apply the monotone convergence theorem with bound m(E)
2- If E has infinite measure you have to prove that for which just use that pointwise convergence implies convergence in measure so that you can bound below your seuqence (of integrals) by somethig which goes to infinity.