Let \(G\) be an open set. Define the Sobolev spaces \(H^m(G)\), \(m=1,2,\cdots \), and \(H_0^m(G)\), \(m=1,2,\cdots \). Indicate why
these spaces are Hilbert spaces.
Let \(G\) be a bounded open set. State and prove Poincaré’s inequality for
functions \(u\in H_0^1(G)\) and thus verify that \(H_0^1(G)\) is also a Hilbert space with respect to the
inner product \[ (u,v)_{H_0^1(G)}=\int _G \nabla u\cdot \overline {\nabla v}\,dx. \]