@article{RCM_1976__10_181652,
     author = {D. K. Rao},
     title = {A triangle inequality for angles in a {Hilbert} space},
     journal = {Revista colombiana de matematicas},
     pages = {95--98},
     publisher = {mathdoc},
     volume = {10},
     year = {1976},
     zbl = {0349.46021},
     url = {http://geodesic.mathdoc.fr/item/RCM_1976__10_181652/}
}