code: def normalize_fulltext(fulltext):
      
      # We recognize keywords by the spaces. We need these to match the
      # first and last words of the document.
      fulltext = " " + fulltext + " "
  
      # Replace some weird unicode characters.
      fulltext = replace_undesirable_characters(fulltext)
      # Replace the greek characters by their name.
      fulltext = _replace_greek_characters(fulltext)
  
      washing_regex = get_washing_regex()
  
      # Apply the regular expressions to the fulltext.
      for regex, replacement in washing_regex:
          fulltext = regex.sub(replacement, fulltext)
  
      return fulltext
docs: Return a 'cleaned' version of the output provided by pdftotext.