(define (avant? la-date date-ref)
  (or (< (annee la-date) (annee date-ref))
      (and (= (annee la-date) (annee date-ref))
	   (< (mois la-date) (mois date-ref)))
      (and (= (annee la-date) (annee date-ref))
	   (= (mois la-date) (mois date-ref))
	   (< (jour la-date) (jour date-ref)))))