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@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/} }
D. K. Rao. A triangle inequality for angles in a Hilbert space. Revista colombiana de matematicas, Tome 10 (1976), pp. 95-98. http://geodesic.mathdoc.fr/item/RCM_1976__10_181652/