#lang racket

(define (lex<? a b)
  (cond ((null? b) #f)
        ((null? a) #t)
        ((= (car a) (car b)) (lex<? (cdr a) (cdr b)))
        (else (< (car a) (car b)))))

(lex<? '(1 2 3 4 5) '(1 2 3 4 4)) ; -> #f