contract Owner {
    /**
    * @dev Get smart contract's owner
    * @return The owner of the smart contract
    */
    function owner() public view returns (address);
    
    //check address is a valid owner (owner or coOwner)
    function isValidOwner(address _address) public view returns(bool);

}
/**
 * @title Utility interfaces
 * @author Biglabs Pte. Ltd.
 * @dev Smart contract with owner
 */
function owner() public view returns (address);

/**
 * @dev Get smart contract's owner
 * @return The owner of the smart contract
 */