# Sobolev Space Notation Question

Hi my lecturer for Functional Analysis has used the following notation when talking about Sobolev spaces: $$\overset{\circ}{W}\vphantom{W}^m(\Omega) = \overline{\mathcal{C^{\infty}_0}(\Omega)}^{W^m(\Omega)}$$ $W^m(\Omega)$ is the notation for a Sobolev space but I get lost when the above notation is introduced to define a new space. I know that it consists of functions which are zero at the boundary but I just dont understand what is happening in the above notation when defining it. Could someone please give me a rundown of what this notation actually means?

$V:=\mathcal C_0^\infty$ is a subspace of $W^m(\Omega)$. There is a topology on $W^m(\Omega)$ given by a norm. Then we take the closure of $V$ with respect to this norm, and this gives by definition $W^m_0(\Omega)$.
• A norm $N$ gives a metric, namely $d(x,y):=N(x-y)$, and a metric gives a topology. – Davide Giraudo Feb 17 '13 at 16:12