contract StandardToken is ERC20, BasicToken {
  // public variables

  // internal variables
  mapping (address => mapping (address => uint256)) _allowances;

  // events

  // public functions
  function transferFrom(address from, address to, uint256 value) public returns (bool) {
    require(to != address(0));
    require(value <= _balances[from]);
    require(value <= _allowances[from][msg.sender]);

    _balances[from] = _balances[from].sub(value);
    _balances[to] = _balances[to].add(value);
    _allowances[from][msg.sender] = _allowances[from][msg.sender].sub(value);
    emit Transfer(from, to, value);
    return true;
  }

  function approve(address agent, uint256 value) public returns (bool) {
    _allowances[msg.sender][agent] = value;
    emit Approval(msg.sender, agent, value);
    return true;
  }

  function allowance(address owner, address agent) public view returns (uint256) {
    return _allowances[owner][agent];
  }

  function increaseApproval(address agent, uint value) public returns (bool) {
    _allowances[msg.sender][agent] = _allowances[msg.sender][agent].add(value);
    emit Approval(msg.sender, agent, _allowances[msg.sender][agent]);
    return true;
  }

  function decreaseApproval(address agent, uint value) public returns (bool) {
    uint allowanceValue = _allowances[msg.sender][agent];
    if (value > allowanceValue) {
      _allowances[msg.sender][agent] = 0;
    } else {
      _allowances[msg.sender][agent] = allowanceValue.sub(value);
    }
    emit Approval(msg.sender, agent, _allowances[msg.sender][agent]);
    return true;
  }

  // internal functions
}
function transferFrom(address from, address to, uint256 value) public returns (bool) {
  require(to != address(0));
  require(value <= _balances[from]);
  require(value <= _allowances[from][msg.sender]);

  _balances[from] = _balances[from].sub(value);
  _balances[to] = _balances[to].add(value);
  _allowances[from][msg.sender] = _allowances[from][msg.sender].sub(value);
  emit Transfer(from, to, value);
  return true;
}

// events
// public functions