...act KittyBase is KittyAccessControl
contract KittyOwnership is KittyBase, ERC721
contract KittyBreeding is KittyOwnership
contract KittyAuction is KittyBreeding
contract KittyMinting is KittyAuction
contract KittyCore is KittyMinting
```
所以`KittyCore`最终是应用程序指向的合约...
...ier: MIT
pragma solidity 0.8.20;
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
contract A is ERC20{
constructor()ERC20("",""){}
//check a address is a contract
function checkContract(address addr)public view returns(bool){
uint size;
//以太坊的...