/*
 * This code is from "Algorithms in C, Third Edition,"
 * by Robert Sedgewick, Addison Wesley Longman, 1998.
 */
void sortR(link h, void (*visit)(Item))
  { 
    if (h == z) return;
    sortR(h->l, visit);
    visit(h->item); 
    sortR(h->r, visit);
  }
void STsort(void (*visit)(Item))
  { sortR(head, visit); }