docs: private void putRec(O obj, Rec<O> rec) {
      graph.put(obj, rec);
      for(int i = 0; i < numelems; ++i) {
        if(obj == elems[i]) {
          return;
        }
      }
      if(elems.length == numelems) {
        elems = Arrays.copyOf(elems, (elems.length << 1) + 1);
      }
      elems[numelems++] = obj;
    }