no. 1
Properties of hypersurfaces which are characteristic for spaces of constant curvature
Annali della Scuola Normale Superiore di Pisa - Scienze Fisiche e Matematiche, Série 3, Tome 26 (1972) no. 1, pp. 233-245. 
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     author = {Kowalski, Old\v{r}ich},
     title = {Properties of hypersurfaces which are characteristic for spaces of constant curvature},
     journal = {Annali della Scuola Normale Superiore di Pisa - Scienze Fisiche e Matematiche},
     pages = {233--245},
     publisher = {Scuola normale superiore},
     volume = {Ser. 3, 26},
     number = {1},
     year = {1972},
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     zbl = {0233.53009},
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Kowalski, Oldřich. Properties of hypersurfaces which are characteristic for spaces of constant curvature. Annali della Scuola Normale Superiore di Pisa - Scienze Fisiche e Matematiche, Série 3, Tome 26 (1972) no. 1, pp. 233-245. http://archive.numdam.org/item/ASNSP_1972_3_26_1_233_0/

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