Unary alphabet equal
Unary alphabet not equal
Unary alphabet one character
Binary alphabet, interlacing variants:
- One word ends in b^k and no other b^k substring, other word is b^ja for various j near k. 
- Variants on that, make sure b^(k-1) is a substring too.
- All of those cases, but with a ternary alphabet.
- Throw in some other substrings. Throw in non-substrings of the form ab^ja
One word is a substring of the other (different alphabet sizes)
Random cases