@article{MAN_1965__159_182694,
     author = {I. SINGER},
     title = {On the {Extension} of {Continuous} {Linear} {Functionals} and {Best} {Approximation} in {Normed} {Linear} {Spaces.}},
     journal = {Mathematische Annalen},
     pages = {344--355},
     publisher = {mathdoc},
     volume = {159},
     year = {1965},
     zbl = {0141.12002},
     url = {http://geodesic.mathdoc.fr/item/MAN_1965__159_182694/}
}