@article{JCA_1997_4_2_a1,
     author = {R. A. Poliquin and R. T. Rockafellar},
     title = {Proto-Derivatives of {Partial} {Subgradient} {Mappings}},
     journal = {Journal of convex analysis},
     pages = {221--234},
     publisher = {mathdoc},
     volume = {4},
     number = {2},
     year = {1997},
     url = {http://geodesic.mathdoc.fr/item/JCA_1997_4_2_a1/}
}