code: func (rh *rowHeap) Less(i, j int) bool {
  	l := rh.ims[i].value.key
  	r := rh.ims[j].value.key
  	ret, err := lessThan(rh.sc, l, r, rh.byDesc)
  	if rh.err == nil {
  		rh.err = err
  	}
  	return ret
  }
docs: // Less implements heap.Interface Less interface.