/*
 * This code is from "Algorithms in C, Third Edition,"
 * by Robert Sedgewick, Addison Wesley Longman, 1998.
 */
link joinLR(link a, link b)
  { 
    if (a == z) return b;
    if (b == z) return a;
    if (rand()/(RAND_MAX/(a->N+b->N)+1) < a->N)
         { a->r = joinLR(a->r, b); return a; }
    else { b->l = joinLR(a, b->l); return b; }
  }
link deleteR(link h, Key v)
  { link x; Key t = key(h->item);
    if (h == z) return z; 
    if (less(v, t)) h->l = deleteR(h->l, v);
    if (less(t, v)) h->r = deleteR(h->r, v);
    if (eq(v, t)) 
      { x = h; h = joinLR(h->l, h->r); free(x); }
    return h;
  }
void STdelete(Key v)
  { head = deleteR(head, v); }