function burn(uint256 _value) public returns (bool success) {
        
        require(locked[msg.sender] == 0);
        
        
        require(balances[msg.sender] >= _value);
        
        
        balances[msg.sender] -= _value;
        
        
        totalSupply -= _value;
        Burn(msg.sender, _value);
        return true;
    }