code: private double spfL(InfoTree it1, InfoTree it2) {
  
  		int fPostorder = it1.getCurrentNode();
  		int gPostorder = it2.getCurrentNode();
  
  		int minKR = it2.info[POST2_MIN_KR][gPostorder];
  		int[] kr = it2.info[KR];
  		if (minKR > -1) {
  			for (int j = minKR; kr[j] < gPostorder; j++) {
  				treeEditDist(it1, it2, fPostorder, kr[j]);
  			}
  		}
  		treeEditDist(it1, it2, fPostorder, gPostorder);
  
  		return it1.isSwitched() ? delta[gPostorder][fPostorder]
  				+ deltaBit[gPostorder][fPostorder] * costMatch
  				: delta[fPostorder][gPostorder]
  						+ deltaBit[fPostorder][gPostorder] * costMatch;
  	}
docs: Single-path function for the left-most path based on Zhang and Shasha
  algorithm.
  
  @param it1
  @param it2
  @return distance between subtrees it1 and it2