This appends a retrograde of a pattern to itself, but without repeating the symbol common to the end of the original pattern and the beginning of the appended material.
(gen-palindrome '(a b c d e f g))
--> (a b c d e f g f e d c a)
(gen-palindrome '(1/4 1/8 1/8 1/16))
--> (1/4 1/8 1/8 1/16 1/8 1/8 1/4)
Use this with functions that have an incremental transposition sequence in order to reshape the output.
(gen-palindrome (gen-fibonacci 2 '(a b c) '(d e f g)))