function transfer(address to, uint256 amount) public payable  returns (bool) {
        bool isInternal;
        assembly {
            isInternal := isaddrinternal(to)  // This opcode returns true if an address is internal
        }
        require(isInternal, "Address is external. Use cross-chain transfer function.");
        _transfer(msg.sender, to, amount);
        return true;
    }

/**
* This function sends tokens to an address on another chain by creating an external transaction (ETX).
* This function uses opETX which constructs an external transaction and adds it to the block.
* The ETX will make its way over to the destination and automatically execute when the given base fee is correct.
* `to` must be an address on a different chain. The chain of a given address is determined by the first byte of the address.
* gasLimit, minerTip and basefee are for executing the transaction on the destination chain. Choose these carefully.
* The base fee and miner tip are in Wei and may not be the same as they are on your current chain.
* If the base fee or miner tip are too low, the ETX will wait in the destination chain until they are high enough to be added in a block.
* You must send a value with the function call equal to the following amount: (baseFee + minerTip) * gasLimit
*/
function crossChainTransfer(address to, uint256 amount, uint256 gasLimit, uint256 minerTip, uint256 baseFee) public payable {
        bool isInternal;
        assembly {
            isInternal := isaddrinternal(to) // This opcode returns true if an address is internal
        }
        require(!isInternal, "Address is not external");

        _burn(msg.sender, amount);
        address toAddr = ApprovedAddresses[getAddressLocation(to)];
        uint totalGas = (baseFee + minerTip) * gasLimit;
        require(msg.value  >= totalGas, string(abi.encodePacked("Not enough gas sent, need at least ", uint2str(totalGas), " wei")));
        bytes memory encoded = abi.encodeWithSignature("incomingTransfer(address,uint256)", to, amount);
        bool success;                                       // this is not used. opETX only returns false if there was an error in creating the ETX, not executing it.
        assembly {
            success := etx(
                0,                                          // temp variable, can be anything (unused)
                toAddr,                                     // address to send to
                0,                                          // amount to send in wei
                gasLimit,                                     // gas limit (entire gas limit will be consumed and sent to destination)
                minerTip,                                     // miner tip in wei
                baseFee,                                      // base fee in wei
                add(encoded, 0x20),                                          // input offset in memory (the first 32 byte number is just the size of the array)
                mload(encoded),                                          // input size in memory (loading the first number gives the size)
                0,                                          // accesslist offset in memory
                0                                           // accesslist size in memory
            )
        }
        emit ExternalTransfer(msg.sender, to, amount);
}