def lemmatize(self, tokens):
        """define list of lemmas"""
        entries = self.entries
        forms_and_lemmas = self.forms_and_lemmas

        lemma_list = [x[0] for x in entries]
        """Provide a lemma for each token"""
        lemmatized = []
        for token in tokens:
            """check for a match between token and list of lemmas"""
            if token in lemma_list:
                lemmed = (token, token)
                lemmatized.append(lemmed)
            else:
                """if no match check for a match between token and list of lemma forms"""
                lemma = [k for k, v in forms_and_lemmas.items() if token in v]
                if lemma != []:
                    lemmed = (token, lemma)
                    lemmatized.append(lemmed)
                elif lemma == []:
                    """if no match apply regular expressions and check for a match against the list of lemmas again"""
                    regexed = regex(token)
                    if regexed in lemma_list:
                        lemmed = (token, regexed)
                        lemmatized.append(lemmed)
                    else:
                        lemmed = (token, "None")
                        lemmatized.append(lemmed)
        return lemmatized
define list of lemmas