contract Governable {
    address public governor;

    event ChangeGovernor(address indexed _old, address indexed _new);

    modifier onlyGovernor() {
        require(msg.sender == governor, 'Governable: FORBIDDEN');
        _;
    }

    // called after deployment
    function initGovernorAddress(address _governor) internal {
        require(_governor != address(0), 'Governable: INPUT_ADDRESS_IS_ZERO');
        governor = _governor;
    }

    function changeGovernor(address _new) public onlyGovernor {
        _changeGovernor(_new);
    }

    function _changeGovernor(address _new) internal {
        require(_new != address(0), 'Governable: INVALID_ADDRESS');
        require(_new != governor, 'Governable: NO_CHANGE');
        address old = governor;
        governor = _new;
        emit ChangeGovernor(old, _new);
    }

}
// Dependency file: contracts/modules/Governable.sol
// pragma solidity >=0.5.16;
function initGovernorAddress(address _governor) internal {
        require(_governor != address(0), 'Governable: INPUT_ADDRESS_IS_ZERO');
        governor = _governor;
    }
// called after deployment