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contracts...Ownable.sol

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

contract Ownable {
    address public owner;
    
    modifier onlyOwner() {
        require(owner == msg.sender, "Not invoked by the owner");
        _;
    }
    
    constructor() {
        owner = msg.sender;
    }
}