@article{10_4064_sm159_2_7,
     author = {Piotr Haj{\l}asz},
     title = {A new characterization of the {Sobolev} space},
     journal = {Studia Mathematica},
     pages = {263--275},
     publisher = {mathdoc},
     volume = {159},
     number = {2},
     year = {2003},
     doi = {10.4064/sm159-2-7},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/sm159-2-7/}
}