interface IERC20 {
  function totalSupply() external view returns (uint256); //ERC20Basic
  function balanceOf(address account) external view returns (uint256); //ERC20Basic
  function transfer(address recipient, uint256 amount) external returns (bool);//ERC20Basic
  function allowance(address owner, address spender) external view returns (uint256);//ERC20
  function approve(address spender, uint256 amount) external returns (bool);//ERC20
  function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);//ERC20
  event Transfer(address indexed from, address indexed to, uint256 value);//ERC20Basic
  event Approval(address indexed owner, address indexed spender, uint256 value);//ERC20
}
function approve(address spender, uint256 amount) external returns (bool);//ERC20

//ERC20