@article{DCG_1994__12_1_131334,
     author = {M. Sharir and D. Halperin},
     title = {New {Bounds} for {Lower} {Envelopes} in {Three} {Dimensions,} with {Applications} to {Visibility} in {Terrains.}},
     journal = {Discrete & computational geometry},
     pages = {313--326},
     publisher = {mathdoc},
     volume = {12},
     number = {1},
     year = {1994},
     zbl = {0819.68136},
     url = {http://geodesic.mathdoc.fr/item/DCG_1994__12_1_131334/}
}