private static String getIrregularPastParticiple(String verb) {
    String irregularVerb = IRREGULAR_VERBS.get(verb);
    if (irregularVerb != null) return irregularVerb;
    for (String prefix : PREFIXES) {
      if (verb.startsWith(prefix)) {
        irregularVerb = IRREGULAR_VERBS.get(verb.substring(prefix.length()));
        if (irregularVerb !=  null) return prefix + irregularVerb;
      }
    }
    return null;
  }
private static String getIrregularPastParticiple(String verb)