code: def choose_tag(self: object, tokens: List[str], index: int, history: List[str]):
          
          keys = self.lemmas.keys()
          if tokens[index] in keys:
              return self.lemmas[tokens[index]]
docs: Looks up token in ``lemmas`` dict and returns the corresponding
          value as lemma.
          :rtype: str
          :type tokens: list
          :param tokens: List of tokens to be lemmatized
          :type index: int
          :param index: Int with current token
          :type history: list
          :param history: List with tokens that have already been lemmatized; NOT USED