abstract contract ERC20 {
    using SafeMath for uint256;

    uint256 internal _totalSupply;
    mapping(address => uint256) internal _balances;
    mapping(address => mapping(address => uint256)) internal _allowances;

    event Transfer(address indexed from, address indexed to, uint256 amount);
    event Approval(
        address indexed owner,
        address indexed spender,
        uint256 amount
    );

    /*
   * Internal Functions for ERC20 standard logics
   */

    function _transfer(address from, address to, uint256 amount)
        internal
        returns (bool success)
    {
        _balances[from] = _balances[from].sub(
            amount,
            "ERC20/transfer : cannot transfer more than token owner balance"
        );
        _balances[to] = _balances[to].add(amount);
        emit Transfer(from, to, amount);
        success = true;
    }

    function _approve(address owner, address spender, uint256 amount)
        internal
        returns (bool success)
    {
        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
        success = true;
    }

    function _mint(address recipient, uint256 amount)
        internal
        returns (bool success)
    {
        _totalSupply = _totalSupply.add(amount);
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(address(0), recipient, amount);
        success = true;
    }

    function _burn(address burned, uint256 amount)
        internal
        returns (bool success)
    {
        _balances[burned] = _balances[burned].sub(
            amount,
            "ERC20Burnable/burn : Cannot burn more than user's balance"
        );
        _totalSupply = _totalSupply.sub(
            amount,
            "ERC20Burnable/burn : Cannot burn more than totalSupply"
        );
        emit Transfer(burned, address(0), amount);
        success = true;
    }

    /*
   * public view functions to view common data
   */

    function totalSupply() external view returns (uint256 total) {
        total = _totalSupply;
    }
    function balanceOf(address owner) external view returns (uint256 balance) {
        balance = _balances[owner];
    }

    function allowance(address owner, address spender)
        external
        view
        returns (uint256 remaining)
    {
        remaining = _allowances[owner][spender];
    }

    /*
   * External view Function Interface to implement on final contract
   */
    function name() virtual external view returns (string memory tokenName);
    function symbol() virtual external view returns (string memory tokenSymbol);
    function decimals() virtual external view returns (uint8 tokenDecimals);

    /*
   * External Function Interface to implement on final contract
   */
    function transfer(address to, uint256 amount)
        virtual
        external
        returns (bool success);
    function transferFrom(address from, address to, uint256 amount)
        virtual
        external
        returns (bool success);
    function approve(address spender, uint256 amount)
        virtual
        external
        returns (bool success);
}
function name() virtual external view returns (string memory tokenName);
/*
 * External view Function Interface to implement on final contract
 */