Case number 26

Boy's surface with three critical points Möbius strip with a sphere as boundary curve Infinitesimal neighbourhood of a line congruence Infinitesimal neighbourhood of a line congruence
Infinitesimal neighbourhood of a line congruence Bruhat-Tits building Zeiss stereoscope
Stereoscopic pictures of crystal grids from v. Laue and v. Mises 2 stereoscopes 2 stereoscopes

The corresponding bottom case is: Case number U 26

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