no. 2
Ellipsoids and hyperboloids with infinite foci
Compositio Mathematica, Tome 52 (1984) no. 2, pp. 231-244 
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     author = {Im Hof, Hans-Christoph},
     title = {Ellipsoids and hyperboloids with infinite foci},
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     pages = {231--244},
     year = {1984},
     publisher = {Martinus Nijhoff Publishers},
     volume = {52},
     number = {2},
     mrnumber = {750359},
     zbl = {0544.53034},
     language = {en},
     url = {https://www.numdam.org/item/CM_1984__52_2_231_0/}
}
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Im Hof, Hans-Christoph. Ellipsoids and hyperboloids with infinite foci. Compositio Mathematica, Tome 52 (1984) no. 2, pp. 231-244. https://www.numdam.org/item/CM_1984__52_2_231_0/

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