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contracts...Mappings.sol

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

contract Mappings {
    mapping(address => uint256) private luckyNumbers;

    function getMyLuckyNumber() external view returns(uint256) {
        require(luckyNumbers[msg.sender] != 0, "0 can't be lucky");

        return luckyNumbers[msg.sender];
    }

    function setMyLuckyNumber(uint256 number) external {
        require(number > 0, "Can't be set to zero");

        luckyNumbers[msg.sender] = number;
    }
}