@article{MOMA_1979__88_177926,
     author = {Ivan Singer and Pier L. Papini},
     title = {Best {Coapproximation} in {Normed} {Linear} {Spaces.}},
     journal = {Monatshefte f\"ur Mathematik},
     pages = {27--44},
     publisher = {mathdoc},
     volume = {88},
     year = {1979},
     zbl = {0421.41017},
     url = {http://geodesic.mathdoc.fr/item/MOMA_1979__88_177926/}
}