(define interleave
(lambda (lst1 lst2)
(if (null? lst1)
lst2
(cons (car lst1)
(interleave lst2 (cdr lst1))))))
To interleave two halves of the list deck, use
first-elements-of and list-tail:
(interleave (first-elements-of 26 deck)
(list-tail deck 26))