A luggage includes a retaining device for easily hooking a handle of an auxiliary bag to the luggage. The first spectral element is placed at the front focal point of a first lens, the reflecting member is placed at a position where the back focal point of the first lens coincides with the front focal point of a second lens, and the second spectral element is placed at the back focal point of the second lens. Internal derivation of the reference signal is accomplished by suppressing the desired signal included within a sampled quantum of a composite signal. The mop head may have a pad of material intended, in use, to be brought into contact with the surface to be cleaned. Input temporal image-samples are temporally interpolated to create the output sequence and an intentional, periodic motion-judder component that is visible when the output temporal image-samples are displayed is introduced.