@article{00821691, title = {On a characterization of circles and spheres.}, journal = {Beitr\"age zur Algebra und Geometrie}, volume = {36}, year = {1995}, pages = {211-218}, zbl = {0844.52003}, language = {en}, url = {http://dml.mathdoc.fr/item/00821691} }
Groemer, H. On a characterization of circles and spheres.. Beiträge zur Algebra und Geometrie, Tome 36 (1995) pp. 211-218. http://gdmltest.u-ga.fr/item/00821691/