"Impossible" objects are those that are impossible in three
dimensions, but can be created in two dimensions to make an illusion
in three dimensions. The cube displayed on the stamp below is used by
M. C. Escher in both Man with Cuboid and Belvedere, from
1958. In Belvedere the structure also is based on the
impossible cube. Waterfall, 1961, also explores the cube.
The three stamps from
Sweden show work by Oscar Reutervärd, a Swedish artist. In 1934 he
drew the first impossible triangle, using nine cubes. This figure, is
titled Opus 1.