Maps a list of token ids to the corresponding term ids
        @type list_tokens: list
        @param list_tokens: list of token identifiers
        @rtype: list
        @return: list of term idenfitiers

def map_tokens_to_terms(self,list_tokens):
        """
        Maps a list of token ids to the corresponding term ids
        @type list_tokens: list
        @param list_tokens: list of token identifiers
        @rtype: list
        @return: list of term idenfitiers
        """
        if self.terms_for_token is None:
            self.terms_for_token = {}
            for term in self.get_terms():
                termid = term.get_id()
                token_ids = term.get_span().get_span_ids()
                for tokid in token_ids:
                    if tokid not in self.terms_for_token:
                        self.terms_for_token[tokid] = [termid]
                    else:
                        self.terms_for_token[tokid].append(termid)

        ret = set()
        for my_id in list_tokens:
            term_ids = self.terms_for_token.get(my_id,[])
            ret |= set(term_ids)
        return sorted(list(ret))