public boolean sortedBetween (E[] array, int left, int right) {
  assert array != null         : "precondition";
  assert left >= 0             : "precondition";
  assert right < array.length  : "precondition";
 
  if( left >= right 
      || ! array[left].compareTo(array[left + 1]) <= 0)) { 
    return left == right;
  }
 
  return sortedBetween(array, left++, right);
}