code: func (ps *peerSet) PeersWithoutBlock(hash common.Hash) []*peer {
  	ps.lock.RLock()
  	defer ps.lock.RUnlock()
  
  	list := make([]*peer, 0, len(ps.peers))
  	for _, p := range ps.peers {
  		if !p.knownBlocks.Contains(hash) {
  			list = append(list, p)
  		}
  	}
  	return list
  }
docs: // PeersWithoutBlock retrieves a list of peers that do not have a given block in
  // their set of known hashes.