def possible_words str,i
      ret=@word_dic.possible_words str,i
      ret.concat(@unk_dic.possible_words(str,i,!ret.empty?))
      ret
    end
def possible_words str,i
      ret=@word_dic.possible_words str,i
      ret.concat(@unk_dic.possible_words(str,i,!ret.empty?))
      ret
    end
-> [Word]