code: func (p *peerConnection) Lacks(hash common.Hash) bool {
  	p.lock.RLock()
  	defer p.lock.RUnlock()
  
  	_, ok := p.lacking[hash]
  	return ok
  }
docs: // Lacks retrieves whether the hash of a blockchain item is on the peers lacking
  // list (i.e. whether we know that the peer does not have it).