In this task, you are given two strings A,B. Find the longer of the two lists, convert it to lowercase, and return all the unique alphabets used in it. The two input strings are never equal.

FLYYRxXtDEyJSLLYb, TWXXtDEyJYKUhaU
b, d, e, f, j, l, r, s, t, x, y

ZhcqaFYRsKplQz, SbTucqaFYRsKdIaTz
a, b, c, d, f, i, k, q, r, s, t, u, y, z

TwBKlZtZOCoubwQXxUnaCKWxLFsDq, HnGqJPRFQtZOCoubwQXxUnaCfYI

a, b, c, d, f, k, l, n, o, q, s, t, u, w, x, z