@article{10_4153_CMB_1993_005_9,
     author = {Clarke, F. H. and Redheffer, R. M.},
     title = {The {Proximal} {Subgradient} and {Constancy}},
     journal = {Canadian mathematical bulletin},
     pages = {30--32},
     year = {1993},
     volume = {36},
     number = {1},
     doi = {10.4153/CMB-1993-005-9},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1993-005-9/}
}