docs: private static String phrasalVerb(Morphology morpha, String word, String tag) {
          // must be a verb and contain an underscore
          assert (word != null);
          assert (tag != null);
          if (!tag.startsWith(LangLib.POS_VB) || !word.contains("_")) {
              return null;
          }
  
          // check whether the last part is a particle
          String[] verb = word.split("_");
          if (verb.length != 2) {
              return null;
          }
          String particle = verb[1];
          if (particles.contains(particle)) {
              String base = verb[0];
              String lemma = morpha.lemma(base, tag);
              return lemma + '_' + particle;
          }
  
          return null;
      }