The projected image is reflected in a mirror placed at a right angle to the screen. The image of a boxer hitting a punching bag is projected onto the screen in such a way that the bag is at the edge of the frame where it meets the mirror. The mirror, however, creates the effect of the boxer fighting himself

—Roswitha Mueller, VALIE EXPORT: Fragments of the Imagination

Splitscreen is reduction through doubling—two images from one projector. In “The Man with the Camera,” Vertov identifies the act of doubling in Mannerist painting [Da Vinci, Dali, Clerici, Micciota] as a characteristic of cinematography; he liked to be filmed at the edge of store windows.