@article{AFM_2004_29_1_a9,
     author = {Piotr Hajlasz and Jani Onninen},
     title = {On boundedness of maximal functions in {Sobolev} spaces},
     journal = {Annales Fennici Mathematici},
     pages = {167--176},
     publisher = {mathdoc},
     volume = {29},
     number = {1},
     year = {2004},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/AFM_2004_29_1_a9/}
}