Kata

Task

In this kata, your job is to return a lazy sequence consisting of strings containing the letters of the alphabet in both lowercase and uppercase.

Sequence

The sequence follows a recursive pattern:

• first return each letter of the alphabet (lowercase before uppercase)
• then return each letter of the alphabet appended to each element retrieved from a recursive call to the sequence
• the sequence is infinite

a, b, c, ... y, z, A, B, C, ..., Y, Z, aa, ab, ac, ..., az, aA, ..., aZ, ba, bb, ..., bA, ..., bZ, ..., ca, ... cZ, ...
......, Za, Zb ..., ZZ, aaa, aab, ..., aaZ, aba, abb, ..., abZ, aca, ..., ..., ..., ZZZ, aaaa, aaab, ..

Good luck!