@article{10_4153_CJM_1968_149_8,
     author = {Pfeffer, W. F.},
     title = {On the {Lower} {Derivate} of a {Set} {Function}},
     journal = {Canadian journal of mathematics},
     pages = {1489--1498},
     year = {1968},
     volume = {20},
     number = {1},
     doi = {10.4153/CJM-1968-149-8},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1968-149-8/}
}