1  Path-to-blue-eyes

(define-struct ft (name eye-color mom dad))

;; path-to-blue-eyes : family-tree  list-of-symbols or #f
;; finds the path to a blue eyed ancestor
(define (path-to-blue-eyes ft)
  (cond
    [(eq? ft 'unknown) #f]
    [else
     (if (eq? (ft-eye-color ft) 'blue)
         '()
         (let ([mom-path (path-to-blue-eyes (ft-mom ft))]
               [dad-path (path-to-blue-eyes (ft-dad ft))])
           (cond
             [(and mom-path dad-path) (cons 'mom mom-path)]
             [(and mom-path (not dad-path)) (cons 'mom mom-path)]
             [(and dad-path (not mom-path)) (cons 'dad dad-path)]
             [else #f])))]))

(define tutu (make-ft 'emily 'brown 'unknown 'unknown))
(define opa (make-ft 'bruce 'blue 'unknown 'unknown))
(define mom (make-ft 'alice 'green tutu opa))
(define dad (make-ft 'bill 'brown 'unknown 'unknown))
(define me (make-ft 'robby 'hazel mom dad))

(path-to-blue-eyes me)