code: public static SkippableIterator reverseflatand(SkippableIterator... bitmap) {
  		if (bitmap.length == 0)
  			throw new RuntimeException("nothing to process");
  		SkippableIterator answer = bitmap[bitmap.length - 1];
  		for (int k = bitmap.length - 1; k > 0; --k) {
  			answer = and2by2(answer, bitmap[k]);
  		}
  		return answer;
  	}
docs: Reverseflatand.
  
  @param bitmap
  the bitmap
  @return the skippable iterator