@article{10_4064_cm_34_2_209_217,
     author = {Clyde F. Martin and J. E. Valentine},
     title = {Angles in metric and normed linear spaces},
     journal = {Colloquium Mathematicum},
     pages = {209--217},
     publisher = {mathdoc},
     volume = {34},
     number = {2},
     year = {1975},
     doi = {10.4064/cm-34-2-209-217},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/cm-34-2-209-217/}
}