func: function requestRandom() public payable restricted {
          uint price = proxy.getRandomPrice(RANDOM_GAS);
          require(msg.value >= price);
          uint change = msg.value - price;
          proxy.requestRandom.value(price)(this.random_callback, RANDOM_GAS);
          if (change > 0) {
              msg.sender.transfer(change);
          }
      }