Impossible cube ambiguity present in a Necker cube illustration, in which a cube is drawn with its edges as line segments, and can be interpreted as being in either of two different three-dimensional orientations. An impossible cube is usually rendered as a Necker cube in which the line segments representing the edges have been replaced by what are apparently solid beams. In Escher's print, the top four joints of the cube, and the upper of the two crossings between its beams, match one of the two interpretations of the Necker cube, while the bottom four joints and the bottom crossing match the
The Simple Solution to Rubik's Cube season working out a solution, which he published as a 32-page pamphlet for the university bookstore. It reached the hands of a publisher at Bantam who persuaded Nourse to expand the guide into a 64-page book. The book was published June 1981. It became the best-selling book of 1981, selling 6,680,000 copies that year. It was the fastest-selling title in the 36-year history of Bantam Books. In November 1981 Nourse published a sequel, "The Simple Solutions to Cubic Puzzles", as an aid to the numerous puzzles that were spawned by the Cube-craze. Many later solutions to Rubik's Cube published on