Hänvisningar finns i följande patent|
| US4402510 | 12 feb 1982 | 6 sep 1983 | Nintendo Co., Ltd. | Puzzle toy | | US5224901 | 9 jun 1992 | 6 jul 1993 | The Walt Disney Company | Apparatus and method for displaying an anamorphic illusion | | US5225934 | 12 jun 1992 | 6 jul 1993 | | Kaleidoscope with counter-rotating object wheels | | US7164393 | 5 dec 2002 | 16 jan 2007 | | Display of symmetrical patterns with encoded information |
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