code: func (b *Bitmap) RemoveN(a ...uint64) (changed int, err error) {
  	if len(a) == 0 {
  		return 0, nil
  	}
  
  	changed = b.DirectRemoveN(a...) // modifies a in-place
  
  	if b.OpWriter != nil {
  		op := &op{
  			typ:    opTypeRemoveBatch,
  			values: a[:changed],
  		}
  		if err := b.writeOp(op); err != nil {
  			b.DirectAddN(op.values...) // reset data since we're returning an error
  			return 0, errors.Wrap(err, "writing to op log")
  		}
  	}
  
  	return changed, nil
  }
docs: // RemoveN behaves analagously to AddN.