Welcome to our community

Be a part of something great, join today!

Problem of the Week #289 - May 21, 2019

Status
Not open for further replies.
  • Thread starter
  • Moderator
  • #1

Euge

MHB Global Moderator
Staff member
Jun 20, 2014
1,892
Here is this week's POTW:

-----
Let $(X,\mathcal{M}, \mu)$ be a positive measure space, and let $\{E_n\}$ be a sequence of sets in $\mathcal{M}$ such that $\displaystyle\lim_n \mu(E_n) = 0$. Prove that if $1 \le p \le \infty$, then for all $f\in \mathscr{L}^p(X,\mathcal{M},\mu)$, $\displaystyle\lim_n \int_{E_n} f\, d\mu = 0$.


-----

Remember to read the POTW submission guidelines to find out how to submit your answers!
 
  • Thread starter
  • Moderator
  • #2

Euge

MHB Global Moderator
Staff member
Jun 20, 2014
1,892
No one answered this week's problem. You can read my solution below.

If $q$ is the exponent conjugate to $p$, Hölder's inequality gives $\left\lvert\int_{E_n} f\, d\mu\right\rvert \le \|1_{E_n}\|_{\mathscr{L^q}} \|f\|_{\mathscr{L^p}} = \mu(E_n)^q\, \|f\|_{\mathscr{L^q}} \to 0$ as $n \to \infty$.
 
Status
Not open for further replies.