library Roles {
    struct Role {
        mapping(address => bool) bearer;
    }

    /**
     * @dev Give an account access to this role.
     */
    function add(Role storage _role, address _account) internal {
        require(!has(_role, _account), "Roles: account already has role");
        _role.bearer[_account] = true;
    }

    /**
     * @dev Remove an account's access to this role.
     */
    function remove(Role storage _role, address _account) internal {
        require(has(_role, _account), "Roles: account does not have role");
        _role.bearer[_account] = false;
    }

    /**
     * @dev Check if an account has this role.
     * @return bool
     */
    function has(Role storage _role, address _account) internal view returns (bool) {
        require(_account != address(0), "Roles: account is the zero address");
        return _role.bearer[_account];
    }
}
/**
 * @title Roles
 * @dev Library for managing addresses assigned to a Role.
 */
function has(Role storage _role, address _account) internal view returns (bool) {
        require(_account != address(0), "Roles: account is the zero address");
        return _role.bearer[_account];
    }
/**
 * @dev Check if an account has this role.
 * @return bool
 */