public static double computeStringPairBackoff(String pre,String post,
			 UnigramCountsModel<String> uniqueHash, BigramCountsModel<String,String> bigramHash) {
		Double retVal;
		double augment, denom, prevalue, postvalue;

		prevalue=uniqueHash.get(pre+"<wild>");
		denom=uniqueHash.get("<wild><wild>");
		retVal=bigramHash.get(pre,post);
		augment=-DISCOUNT;
		if (retVal==null || retVal==0) {
		  augment=0;
		}
		postvalue=uniqueHash.get("<wild>"+post);
		augment+=DISCOUNT*(prevalue*postvalue)/denom;	
		return augment;
	  }