docs: public static GrammaticalRelation getPrepC(String prepositionString) {
      GrammaticalRelation result = prepsC.get(prepositionString);
      if (result == null) {
        synchronized(prepsC) {
          result = prepsC.get(prepositionString);
          if (result == null) {
            result = new GrammaticalRelation(Language.English, "prepc", "prepc_collapsed", null, DEPENDENT, prepositionString);
            prepsC.put(prepositionString, result);
            threadSafeAddRelation(result);
          }
        }
      }
      return result;
    }