code: func (ch *Channel) Nack(tag uint64, multiple bool, requeue bool) error {
  	ch.m.Lock()
  	defer ch.m.Unlock()
  
  	return ch.send(&basicNack{
  		DeliveryTag: tag,
  		Multiple:    multiple,
  		Requeue:     requeue,
  	})
  }
docs: /*
  Nack negatively acknowledges a delivery by its delivery tag.  Prefer this
  method to notify the server that you were not able to process this delivery and
  it must be redelivered or dropped.
  
  See also Delivery.Nack
  */