On the density of infinitely differentiable functions in Sobolev spaces for an arbitrary open set. (English. Russian original) Zbl 0313.46033
Proc. Steklov Inst. Math. 131, 39-51 (1974); translation from Trudy Mat. Inst. Steklov 131, 39-50 (1974).
MSC:
46E35 | Sobolev spaces and other spaces of “smooth” functions, embedding theorems, trace theorems |