shellsort(itemType a[], int l, int r)
  { int i, j, k, h; itemType v;
    int incs[16] = { 1391376, 463792, 198768, 86961, 33936,
                     13776, 4592, 1968, 861, 336, 
                     112, 48, 21, 7, 3, 1 };
    for ( k = 0; k < 16; k++)
      for (h = incs[k], i = l+h; i <= r; i++)
        { 
          v = a[i]; j = i;
          while (j >= h && a[j-h] > v)
            { a[j] = a[j-h]; j -= h; }
          a[j] = v; 
        } 
  }