On Burenkov's extension operator preserving Sobolev-Morrey spaces on   Lipschitz domains
  We prove that Burenkov's Extension Operator preserves Sobolev spaces built on general Morrey spaces, including classical Morrey spaces. The analysis concerns bounded and unbounded open sets with Lipschitz boundaries in the n-dimensional Euclidean space. 
Maria Stella Fanciullo and Pier Domenico Lamberti
math.FA