    function transfer(address to, uint value) public returns (bool success) {
        require(_balances[msg.sender] >= value);
        require(to != contractAddress);
        _balances[msg.sender] = _balances[msg.sender].sub(value);
        _balances[to] = _balances[to].add(value);
        emit Transfer(msg.sender, to, value);
        return true;
    }