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

 /** 
  * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender. 
  * 
  * Beware that changing an allowance with this method brings the risk that someone may use both the old 
  * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this 
  * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards: 
  * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729 
  * @param _spender The address which will spend the funds. 
  * @param _value The amount of tokens to be spent. 
  */ 
  function approve(address _spender, uint256 _value) public returns (bool) { 
    allowed[msg.sender][_spender] = _value; 
    Approval(msg.sender, _spender, _value); 
    return true; 
  }

 /** 
  * @dev Function to check the amount of tokens that an owner allowed to a spender. 
  * @param _owner address The address which owns the funds. 
  * @param _spender address The address which will spend the funds. 
  * @return A uint256 specifying the amount of tokens still available for the spender. 
  */ 
  function allowance(address _owner, address _spender) public constant returns (uint256 remaining) { 
    return allowed[_owner][_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 
  */ 
  function increaseApproval (address _spender, uint _addedValue) public returns (bool success) {
    allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);
    Approval(msg.sender, _spender, allowed[msg.sender][_spender]); 
    return true; 
  }

  function decreaseApproval (address _spender, uint _subtractedValue) public returns (bool success) {
    uint oldValue = allowed[msg.sender][_spender]; 
    if (_subtractedValue > oldValue) {
      allowed[msg.sender][_spender] = 0;
    } else {
      allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
    }
    Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;
  }

  function () public payable {
    revert();
  }

}
/** 
 * @title Standard ERC20 token 
 * 
 * @dev Implementation of the basic standard token. 
 * @dev https://github.com/ethereum/EIPs/issues/20 
 * @dev Based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol 
 */
function approve(address _spender, uint256 _value) public returns (bool) { 
    allowed[msg.sender][_spender] = _value; 
    Approval(msg.sender, _spender, _value); 
    return true; 
  }
/** 
 * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender. 
 * 
 * Beware that changing an allowance with this method brings the risk that someone may use both the old 
 * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this 
 * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards: 
 * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729 
 * @param _spender The address which will spend the funds. 
 * @param _value The amount of tokens to be spent. 
 */