contract Invariant {

    // invariants functions
    function invariant_1() public returns (bool) {
        // do something
        return true;
    }

    function invariant_2() public returns (bool) {
        // do something
        return true;
    }
    ...
    
    // test functions
    function test_1() public {
    // do something
    }
    
    function test_2() public {
    // do something
    }
    
    ...
}

// get the call information
function get_caller() external view returns (address);
function get_target() external view returns (address);
function get_value() external view returns (uint256);
function get_data() external view returns (bytes memory);

// get the all contracts that have been called during the transaction
function get_affected_contracts() external view returns (address[] calldata, bytes[] calldata);
// get the all accounts that have been used in IERC20 calls during the transaction (e.g., caller and receiver of transfer)
function get_affected_accounts_ierc20() external view returns (address[] calldata, address[] calldata);

// does last transaction contain a swap?
function contains_swap() external view returns (bool);
// get the all pairs that have been swapped during the transaction
function get_affected_pairs() external view returns (address[] calldata);

// call a contract on state before the transaction
function call_prev_state(address _contract, address caller, bytes memory data, uint256 value) external view returns (bytes memory);
// sell the token on best offer and receive ETH
function sell_token_to_eth_best_path(address token, uint256 amountTokenInWei) external;

// Test only
function test_call(address _contract, address caller, bytes memory data, uint256 value) external returns (bytes memory);

// set ETH balance of an account
function set_balance(address account, uint256 amount) external;
// buy token with ETH
function buy_token(address token, uint256 amountETHInWei) external;

// Print functions
function print_int(string memory key, uint256 i) external;
function print_address(string memory key, address a) external;
function print_string(string memory s) external;

// more functions can be added per demands