contract StandardToken is ERC20, BasicToken {
    mapping (address => mapping (address => uint256)) internal allowed;
    /**
    * @dev Transfer tokens from one address to another
    * @param _from address The address which you want to send tokens from
    * @param _to address The address which you want to transfer to
    * @param _value uint256 the amount of tokens to be transferred
    */
    function transferFrom (
        address _from,
        address _to,
        uint256 _value
    ) public returns (bool)
    {
        require(_to != address(0));
        require(_value <= balances[_from]);
        require(_value <= allowed[_from][msg.sender]);
        balances[_from] = balances[_from].sub(_value);
        balances[_to] = balances[_to].add(_value);
        allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
        
        emit Transfer(_from, _to, _value);
        
        return true;
    }
    function approve(address _spender, uint256 _value) public returns (bool) {
        allowed[msg.sender][_spender] = _value;
        
        emit Approval(msg.sender, _spender, _value);
        
        return true;
    }
    function allowance (
        address _owner,
        address _spender
    )
        public
        view
        returns (uint256)
    {
        return allowed[_owner][_spender];
    }
    function increaseApproval(
        address _spender,
        uint256 _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)
    * @param _spender The address which will spend the funds.
    * @param _subtractedValue The amount of tokens to decrease the allowance by.
    */
    function decreaseApproval(
        address _spender,
        uint256 _subtractedValue
    ) public returns (bool)
    {
        uint256 oldValue = allowed[msg.sender][_spender];
        if (_subtractedValue > oldValue) {
            allowed[msg.sender][_spender] = 0;
        } else {
            allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
        }
        
        emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        
        return true;
    }
}
/**
 * @title Standard ERC20 token
 *
 * @dev Implementation of the basic standard token.
 */
function transferFrom (
    address _from,
    address _to,
    uint256 _value
) public returns (bool)
{
    require(_to != address(0));
    require(_value <= balances[_from]);
    require(_value <= allowed[_from][msg.sender]);
    balances[_from] = balances[_from].sub(_value);
    balances[_to] = balances[_to].add(_value);
    allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
        
    emit Transfer(_from, _to, _value);
        
    return true;
}

/**
 * @dev Transfer tokens from one address to another
 * @param _from address The address which you want to send tokens from
 * @param _to address The address which you want to transfer to
 * @param _value uint256 the amount of tokens to be transferred
 */