contract StandardToken is ERC20, BasicToken {

   mapping (address => mapping (address => uint256)) 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 amout of tokens to be transfered
    */
   function transferFrom(address _from, address _to, uint256 _value) returns (bool) {
     var _allowance = allowed[_from][msg.sender];

     // Check is not needed because sub(_allowance, _value) will already throw if this condition is not met
     // require (_value <= _allowance);

     balances[_to] = balances[_to].add(_value);
     balances[_from] = balances[_from].sub(_value);
     allowed[_from][msg.sender] = _allowance.sub(_value);
     Transfer(_from, _to, _value);
     return true;
   }

   /**
    * @dev Aprove the passed address to spend the specified amount of tokens on behalf of msg.sender.
    * @param _spender The address which will spend the funds.
    * @param _value The amount of tokens to be spent.
    */
   function approve(address _spender, uint256 _value) returns (bool) {

     // To change the approve amount you first have to reduce the addresses`
     //  allowance to zero by calling `approve(_spender, 0)` if it is not
     //  already 0 to mitigate the race condition described here:
     //  https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     require((_value == 0) || (allowed[msg.sender][_spender] == 0));

     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 specifing the amount of tokens still avaible for the spender.
    */
   function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
     return allowed[_owner][_spender];
   }

 }
function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
     return allowed[_owner][_spender];
   }
/**
 * @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 specifing the amount of tokens still avaible for the spender.
 */