| Number | Name | Date | Kind |
|---|---|---|---|
| 1518889 | Wooster | Dec 1924 |
| Number | Date | Country |
|---|---|---|
| 170062 | Dec 1977 | HUX |
| 55-3956 | Jan 1980 | JPX |
| Entry |
|---|
| "Metamagical Themas", by Douglas R. Hofstadter, Scientific American, Mar. 1981, pp. 20-22, 25-28,30,32,35,39. |
| "Notes on Rubik's Magic Cube", by David Singmaster, published by Enslow Publishers, Hillside, N.J., copyright 1981, p. 38, lines 17-23, relied on. |