boolean search(int[] a, first, last, int b)
{
   int middle = (first+last)/2;

   if (middle == first && a[middle]!=b)
      return false;

   if (a[middle] == b)
      return true;

   if (a[middle] < b)
      return search(a, middle, last, b);
   else
      return search(a, first, middle, b);
}