✅ Use VDF to get random-number

1. random Number
   1. block.timestamp, block.difficulty is global val so, anyone can use it!
   2. Chainlinkを使おう！ > こちら

✅ How to use Interface

1. How to use interface

   1. Interface how to use

   interface ICounter {
       function count() external view returns (uint);
   
       function increment() external;
   }
   

   1. Interface(contractAddr).func();

   ICounter(_counter).increment();
   

Ethernaut

How to Call Deployed Contract - Interface | Learn Solidity (0.6)