func: function transferFrom(
      address _from,
      address _to,
      uint256 _value
    )
      public
      returns (bool)
    {
      require(_value <= dataContract.balances(_from));
      require(_value <= allowed[_from][msg.sender]);
      require(_to != address(0));
  
      dataContract.setBalance(_from, dataContract.balances(_from).sub(_value));
      dataContract.setBalance(_to, dataContract.balances(_to).add(_value));
      allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
      emit Transfer(_from, _to, _value);
      return true;
    }