code: public int size(Key low, Key high) {
  	if (low.compareTo(high) > 0)
  	    return 0;
  	if (contains(high))
  	    return rank(high) - rank(low) + 1;
  	else
  	    return rank(high) - rank(low);
      }
docs: Returns the number of keys in the symbol table in the given range.
  
  @param low
  is the lower border.
  @param high
  is the upper border.
  @return the number of keys in the symbol table between <code>low</code>
  (inclusive) and <code>high</code> (exclusive)