@article{JEMS_2008_10_1_a6,
     author = {Hoai-Minh Nguyen},
     title = {Further characterizations of {Sobolev} spaces},
     journal = {Journal of the European Mathematical Society},
     pages = {191--229},
     publisher = {mathdoc},
     volume = {10},
     number = {1},
     year = {2008},
     doi = {10.4171/jems/108},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/jems/108/}
}