docs: private void removeRec(O obj) {
      graph.remove(obj);
      for(int i = 0; i < numelems; ++i) {
        if(obj == elems[i]) {
          System.arraycopy(elems, i + 1, elems, i, --numelems - i);
          elems[numelems] = null;
          return;
        }
      }
    }