(let ((mom-path
        (path-to-blue-eyes
          (ft-mom
            (make-ft
              'robby
              'hazel
              (make-ft
                'alice
                'green
                (make-ft 'emily 'brown 'unknown 'unknown)
                (make-ft 'bruce 'blue 'unknown 'unknown))
              (make-ft 'bill 'brown 'unknown 'unknown)))))
      (dad-path
        (path-to-blue-eyes
          (ft-dad
            (make-ft
              'robby
              'hazel
              (make-ft
                'alice
                'green
                (make-ft 'emily 'brown 'unknown 'unknown)
                (make-ft 'bruce 'blue 'unknown 'unknown))
              (make-ft 'bill 'brown 'unknown 'unknown))))))
  (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)))