Why are the Sobolev spaces $W^{m,p}$ where $m\in\mathbb{Z}$ and $p\in\mathbb{Z}$ with $1\le p\le \infty$ denoted with the letter "$W$"?
I know they are denoted with the letter $H$ when $p=2$ because, in this case, they are Hilbert spaces. However, I don't get the "$W$".
EDIT: does this have a link with the fact their definition involves the so-called "weak derivatives"?