public Integer allTheSameExceptLastItem(AbstractOrderedItemset itemset2) {
		// if these itemsets do not have the same size,  return null
		if(itemset2.size() != this.size()){
			return null;
		}
		// We will compare all items one by one starting from position i =0 to size -1
		for(int i=0; i< this.size(); i++){
			// if this is the last position
			if(i == this.size()-1){ 
				// We check if the item from this itemset is be smaller (lexical order) 
				// and different from the one of itemset2.
				// If not, return null.
				if(this.get(i) >= itemset2.get(i)){  
					return null;
				}
			}
			// If this is not the last position, we check if items are the same
			else if(!this.get(i).equals(itemset2.get(i))){ 
				// if not, return null
				return null; 
			}
		}
		// otherwise, we return the position of the last item
		return itemset2.get(itemset2.size()-1);
	}