code: public boolean isKnown(String word) {
      if (!wordIndex.contains(word))
        return false;
      IntTaggedWord iW = new IntTaggedWord(wordIndex.indexOf(word), nullTag);
      return seenCounter.getCount(iW) > 0.0;
    }
docs: Checks whether a word is in the lexicon. This version works even while
  compiling lexicon with current counters (rather than using the compiled
  rulesWithWord array).
  
  TODO: The previous version would insert rules into the
  wordNumberer.  Is that the desired behavior?  Why not test in
  some way that doesn't affect the index?  For example, start by
  testing wordIndex.contains(word).
  
  @param word The word as a String
  @return Whether the word is in the lexicon