code: func (api *API) IsAddressUsed(address Hash) (bool, error) {
  	var err1, err2 error
  	var states []bool
  	var txs Hashes
  	wg := sync.WaitGroup{}
  	wg.Add(2)
  	go func() {
  		defer wg.Done()
  		states, err1 = api.WereAddressesSpentFrom(address)
  	}()
  	go func() {
  		defer wg.Done()
  		txs, err2 = api.FindTransactions(FindTransactionsQuery{Addresses: Hashes{address}})
  	}()
  	wg.Wait()
  
  	if err := firstNonNilErr(err1, err2); err != nil {
  		return false, err
  	}
  
  	if states[0] || len(txs) > 0 {
  		return true, nil
  	}
  	return false, nil
  }
docs: // IsAddressUsed checks whether an address is used via FindTransactions and WereAddressesSpentFrom.