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contracts...BlockHashRelay.sol

//SPDX-License-Identifier: Unlicense
pragma solidity ^0.8.0;

contract L1Sender {
    address payable immutable l2Receiver;
    
    constructor(address _l2Receiver) {
        l2Receiver = payable(_l2Receiver);
    }
    
    function sendToL2(uint256 numOfHashes) external {
        require(numOfHashes < 256, "MAX_LOOKUP");
        
        uint256 head = block.number-1;
        bytes32[] memory blockHashes = new bytes32[](numOfHashes);
        
        for(uint8 i = 0; i<numOfHashes; i++) {
            blockHashes[i] = blockhash(head-i);
        }
        
        L2Receiver(l2Receiver).receiveFromL1(msg.sender, head, blockHashes);
    }
}

contract L2Receiver {
    address immutable l1Sender;
    uint256 immutable bountyPerBlock;
    mapping(uint256 => bytes32) blockNumToHash;
    
    constructor(uint256 _bountyPerBlock, address _l1Sender) {
        bountyPerBlock = _bountyPerBlock;
        l1Sender = _l1Sender;
    }
    
    function receiveFromL1(address rewardAddress, uint256 head, bytes32[] calldata blockHashes) external {
        require(msg.sender == l1Sender, "NOT_L1_SENDER");
        for(uint256 i = 0; i< blockHashes.length; i++) {
            if(blockNumToHash[head-i] == bytes32(0)) {
                // send bounty if value not set
                (bool success, ) = rewardAddress.call{ value: bountyPerBlock }("");
                require(success, "TRANSFER_FAIL");
            }
            blockNumToHash[head-i] = blockHashes[i];
        }
    }
    
    receive() external payable {}
}