Yea, my assumption is based on static string. However, I'm still not sure what he wants...

Based on what I quoted in my first reply assumption could also be:

- permute all 26 letters in the way that each one appears only once across all [4 letters?] combinations.

Possible? Yes, but you may need a super computer... The factorial of 25 is 1.5511210043 × 10^25