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contracts...sample.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8;

contract ownable{
    address public owner;

    constructor(){
        owner = msg.sender;
    }
    
    modifier onlyOwner{
        require(msg.sender == owner,"not owner");
        _;
    }
    function setOwner(address _newOwner)public onlyOwner{
        require(_newOwner!=address(0),"invalid address");
        owner = _newOwner;
    }

    function onlyOwnerCanAccess() public onlyOwner{
        //code
    }
    function anyoneCanAccess() public{
        //code
    }
}