contract standardToken is EIP20Interface, Ownable {
    using SafeMath for uint;

    mapping (address => uint256) public balances;
    mapping (address => mapping (address => uint256)) public allowed;

    uint8 public constant decimals = 18;  

    string public name;                    
    string public symbol;                
    uint public totalSupply;

    function transfer(address _to, uint _value) public returns (bool success) {
        require(balances[msg.sender] >= _value, "Insufficient balance");
        balances[msg.sender] = balances[msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
        emit Transfer(msg.sender, _to, _value);
        return true;
    }

    function transferFrom(address _from, address _to, uint _value) public returns (bool success) {
        uint allowance = allowed[_from][msg.sender];
        require(balances[_from] >= _value && allowance >= _value);
        balances[_to] = balances[_to].add(_value);
        balances[_from] = balances[_from].sub(_value);
        allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);

        emit Transfer(_from, _to, _value);
        return true;
    }

    function balanceOf(address _owner) public view returns (uint balance) {
        return balances[_owner];
    }

    function approve(address _spender, uint256 _value) public returns (bool success) {
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }

    function allowance(address _owner, address _spender) public view returns (uint256 remaining) {
        return allowed[_owner][_spender];
    }   

    /**
     * @dev Increase the amount of tokens that an owner allowed to a spender. *
     * approve should be called when allowed[_spender] == 0. To increment
     * allowed value is better to use this function to avoid 2 calls (and wait until
     * the first transaction is mined)
     * From MonolithDAO Token.sol
     * @param _spender The address which will spend the funds.
     * @param _addedValue The amount of tokens to increase the allowance by.
     */
    function increaseApproval(address _spender, uint _addedValue) public returns(bool)
    {
        allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);
        emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }
    
    /**
     * @dev Decrease the amount of tokens that an owner allowed to a spender. *
     * approve should be called when allowed[_spender] == 0. To decrement
     * allowed value is better to use this function to avoid 2 calls (and wait until
     * the first transaction is mined)
     * From MonolithDAO Token.sol
     * @param _spender The address which will spend the funds.
     * @param _subtractedValue The amount of tokens to decrease the allowance by.
     */
    function decreaseApproval(address _spender, uint _subtractedValue) public returns(bool)
    {
        uint oldValue = allowed[msg.sender][_spender];
        if (_subtractedValue > oldValue){
            allowed[msg.sender][_spender] = 0;
        } else {
            allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
        }
        return true;
    }
}
/// @dev A standard ERC20 token (with 18 decimals) contract with manager
/// @dev Tokens are initally minted in the contract address
function decreaseApproval(address _spender, uint _subtractedValue) public returns(bool)
    {
        uint oldValue = allowed[msg.sender][_spender];
        if (_subtractedValue > oldValue){
            allowed[msg.sender][_spender] = 0;
        } else {
            allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
        }
        return true;
    }
/**
 * @dev Decrease the amount of tokens that an owner allowed to a spender. *
 * approve should be called when allowed[_spender] == 0. To decrement
 * allowed value is better to use this function to avoid 2 calls (and wait until
 * the first transaction is mined)
 * From MonolithDAO Token.sol
 * @param _spender The address which will spend the funds.
 * @param _subtractedValue The amount of tokens to decrease the allowance by.
 */