Welcome to the CHICKEN Scheme pasting service

(define (largest-sieve lst)
  (cond ((= (null? (car lst)) #t)
          (car lst))
        ((> (car lst) (cadr lst))
          (largest-sieve (cons (car lst) (cddr lst))))
        ((< (car lst) (cadr lst))
          (largest-sieve (cons (cadr lst) (cddr lst))))))

(define (largest-sieve lst)
    (cond ((null? lst) (error "list empty")) ; or 0? depends
             ((null? (car lst)) 0)
             (else (let ((m (max (car lst) (cadr lst))))
                           (largest-sieve (cons max lst) (cddr lst))))))

; untested though