move_down (int data[ ], int first, int last)
{int largest = 2*first+1;

 while (largest <= last) {
 /* LI: All the nodes in the tree rooted at first0,
        except for node first, satisfy the heap property.
        largest is either 2*first+1 or last+1.  
        When largest is last+1, node first satisfies 
        the heap property. */ 
   if (largest < last) /* data[first] has two children */
                       /* (at 2*first+1 and 2*first+2) */ 
     if (data[largest] < data[largest+1])  
                       /* choose larger child */ 
       largest++;
  
   /* swap values if necessary and move down */

   if (data[first] < data[largest]) { 
     swap(data+first, data+largest);
     first = largest; 
     largest = 2*first+1;
     } 
   else largest = last+1; /* to exit the loop: the heap property */ 
   }                      /* isn't violated at data[first];      */ 
}