function burn(uint256 _value) public{
        _burn(msg.sender, _value);
    }
    
    function _burn(address _who, uint256 _value) internal {
        require(_value <= _rOwned[_who]);
        _rOwned[_who] = _rOwned[_who].sub(_value);
        _tTotal = _tTotal.sub(_value);
        emit Transfer(_who, address(0), _value);
    }