[![a 7-by-7 highly symmetric crossword grid with three across and three down lights, each of length 7, intersecting in all even-numbered positions; all odd-numbered positions are unchecked](https://i.sstatic.net/4zaQg.png)](https://i.sstatic.net/4zaQg.png)

###Down
1. _any of_ `bcbbbccccbc` `ccbcbcccbcbcca` `ba` `ccca` `ca` _but none of_ `a` `bcaa`
2. _any of_ `aaaaaaaaac` `aaaaaaaaaaaa` `a2aaaaaa` `a2ac` _but none of_ `2aaaac` `a2aaaacc` `a22ac`
3. _any of_  `234cb` `234b` `23444444cb` `234444444b` _but none of_ `24cb` `24b` `2cb` `3cb` `23cb`

###Across
4. _either of_ `abb` `abbb` _but none of_ `abbbb` `ab` `aabb`
5. _either of_ `]abc` `]abbbbc` _but none of_ `]ac` `]bc` `]ab` `abc` `]]abc`
6. _either of_ `abca` `a` _but none of_ `aa` `aba` `cba` `abba` `bcca`