impossible figure

An impossible figure is an image in two dimensions of an object that, because of spatial inconsistencies, is impossible to realize fully in three dimensions. Among the best known impossible figures are the Penrose triangle, the Penrose stairway, the impossible trident, and the Freemish crate. Notable pioneers of this peculiar form of representation have been Oscar Reutersvärd, Roger Penrose (and his father), and M. C. Escher.