contract StandardToken is ERC20, BasicToken {

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

  /**
   * transfer tokens from one address to another
   */
  function transferFrom(address _from, address _to, uint256 _value) returns (bool) {
    require(_to != address(0));

    var _allowance = allowed[_from][msg.sender];

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

  /**
   * Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
   */
  function approve(address _spender, uint256 _value) returns (bool) {
    // to change the approve amount you first have to reduce the addresses`
    require((_value == 0) || (allowed[msg.sender][_spender] == 0));

    allowed[msg.sender][_spender] = _value;
    Approval(msg.sender, _spender, _value);
    return true;
  }

  /**
   * function to check the amount of tokens that an owner allowed to a spender.
   */
  function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
    return allowed[_owner][_spender];
  }
  
  function increaseApproval (address _spender, uint _addedValue) 
    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) 
    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;
  }

}
/**
 * @title Standard ERC20 token
 * Implementation of the basic standard token.
 */
function approve(address _spender, uint256 _value) returns (bool) {
    // to change the approve amount you first have to reduce the addresses`
    require((_value == 0) || (allowed[msg.sender][_spender] == 0));

    allowed[msg.sender][_spender] = _value;
    Approval(msg.sender, _spender, _value);
    return true;
  }
/**
 * Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
 */