problems D — fill 2-tile gap
| D-1: | 6 ~ x ~ y ~ | 7 (mod = | 8) |
| D-2: | 4 ~ x ~ y ~ | 1 (mod = | 7) |
| D-3: | 5 ~ x ~ y ~ | 2 (mod = | 9) |
| D-4: | 6 ~ x ~ y ~ | 2 (mod = | 10) |
| D-5: | 6 ~ x ~ y ~ | 5 (mod = | 10) |
| D-6: | 6 ~ x ~ y ~ | 4 (mod = | 11) |
| D-7: | 6 ~ x ~ y ~ | 11 (mod = | 12) |
| D-8: | 5 ~ x ~ y ~ | 5 (mod = | 6) |