code: func ParseShard(blob []byte) (Shard, error) {
  	var sorted []string
  	dec := gob.NewDecoder(bytes.NewReader(blob))
  	if err := dec.Decode(&sorted); err != nil {
  		return nil, err
  	}
  	shard := make(Shard, len(sorted))
  	for _, blob := range sorted {
  		shard[blob] = struct{}{}
  	}
  	return shard, nil
  }
docs: // ParseShard deserializes a shard (serialized with Serialize).