docs: public TreeSet<String> getAllPOS() {
  		TreeSet<String> set = new TreeSet<String>(); 
  		Iterator<FNLPDoc> it1 = docs.iterator();
  		while(it1.hasNext()){
  			FNLPDoc doc = it1.next();
  			Iterator<FNLPSent> it2 = doc.sentences.iterator();
  			while(it2.hasNext()){
  				FNLPSent sent = it2.next();
  				if(!sent.hasTag())
  					continue;
  				for(int i=0;i<sent.size();i++){					
  					set.add(sent.tags[i]);
  				}
  			}
  
  		}
  		return set;
  		
  	}