code: function stem_sentence(sentence) {
    for (var i = 0; i < sentence.length; i++) {
      sentence[i] = natural.PorterStemmer.stem(sentence[i]);
    }
    logger.info("stem_sentence: " + sentence);
    return(sentence);
  }
docs: Stem the words of the sentence Not used in the example, because Wordnet cannot recognise all stems