code: def _compute_significant_words(self, document):
      heading_words = map(attrgetter("words"), document.headings)
  
      significant_words = chain(*heading_words)
      significant_words = map(self.stem_word, significant_words)
      significant_words = ffilter(self._is_null_word, significant_words)
  
      return frozenset(significant_words)
  
file_path: sumy/sumy/summarizers/edmundson_title.py
imports: from __future__ import absolute_import
  from __future__ import division, print_function, unicode_literals
  from operator import attrgetter
  from itertools import chain
  from .._compat import ffilter
  from ._summarizer import AbstractSummarizer
label_desc: Use image node_id 3 for calling the EdmundsonTitleMethod obj's underlying member method code with example usage: obj._compute_significant_words(document) and returns: frozenset