The siftup operation is very similar to the the siftup of the basic heap. The main difference being that two versions must exist. One to do a siftup from a max level and one to do a siftup from a min level. The only difference between the two versions is that the ordering relation is reversed.
The correctness of one detail in this program requires extra consideration. When the element c is swapped with its grandparent, the parent(c) is not involved at all. The correctness rests on the fact that since grandparent(c) is on a maxlevel we can be sure that parent(c) is less than grandparent(c), and consequently the heap property remains true when element grandparent(c) is moved to position c.
