(define (heap-merge h1 h2)
  (cond
   [(leaf? h1) h2]
   [(leaf? h2) h1]
   [(< (elem-priority (heap-min h1)) (elem-priority (heap-min h2)))
             (make-node (heap-min h1) (heap-merge h2 (node-right h1)) (node-left h1))]
   [else (make-node (heap-min h2) (heap-merge h1 (node-right h2)) (node-left h2))  ]))