@article{AA_2004_16_6_a4,
     author = {A. Lytchak},
     title = {Differentiation in metric spaces},
     journal = {Algebra i analiz},
     pages = {128--161},
     year = {2004},
     volume = {16},
     number = {6},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/AA_2004_16_6_a4/}
}