Rellich-Kondrachov compactness theorem
Posted: Thu Nov 26, 2015 12:30 am
Let $\mathcal{U} \subset \mathbb{R}^d$ be an open bounded domain. Prove that $H^1(\mathcal{U}) \subset \subset L^2(\mathcal{U})$ ,i.e. the inclusion is compact, where $H^1$ is the Sobolev space $W^{1,2} $ and $L^2$ is our usual space on the corresponding domain.
In other words, show that every uniformly bounded sequence in $H^1(\mathcal{U})$ has a subsequence which is convergent in $L^2(\mathcal{U})$.
(Not easy)
In other words, show that every uniformly bounded sequence in $H^1(\mathcal{U})$ has a subsequence which is convergent in $L^2(\mathcal{U})$.
(Not easy)