(let ((un (if (or #f (number-in-set? 3 (cdr (cons 1 (cons 2 '()))))) (cons 1 (cons 2 '())) (cons (car (cons 3 '())) (cons 1 (cons 2 '())))))) (if (number-in-set? (car (cons 2 (cons 3 '()))) un) un (cons (car (cons 2 (cons 3 '()))) un)))