code: public FutureOperation subscribeExecutedTrades(final BitfinexExecutedTradeSymbol tradeSymbol) {
  
  		final FutureOperation future = new FutureOperation(tradeSymbol);
  		pendingSubscribes.registerFuture(future);
  		
  		final SubscribeTradesCommand subscribeOrderbookCommand
  			= new SubscribeTradesCommand(tradeSymbol);
  		
  		client.sendCommand(subscribeOrderbookCommand);
  		
  		return future;
  	}
docs: Subscribe a executed trade channel
  @param currencyPair
  @param orderBookPrecision
  @param orderBookFrequency
  @param pricePoints
  @return