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 Mechanical puzzle
 A mechanical puzzle is a puzzle presented as a set of mechanically interlinked pieces in which the solution is to manipulate the whole object or parts of it. One of the most well-known mechanical puzzles is Erno Rubik’s Cube that he invented in 1974. The puzzles are mostly designed for a single player where the goal is for the player to see through the principle of the object, not so much that they accidentally come up with the right solution through trial and error. With this in mind, they are often used as an intelligence test or in problem solving training. In 1893, Angelo John Lewis, using the pen name "Professor Hoffman", wrote a book called Puzzles; Old and New. It contained, among other things, more than 40 descriptions of puzzles with secret opening mechanisms. This book grew into a reference work for puzzle games and modern copies exist for those interested. In this category, the puzzle is present in component form, and the aim is to produce a certain shape. The Soma cube made by Piet Hein, the Pentomino by Solomon Golomb and the aforementioned laying puzzles Tangram and "Anker-puzzles" are all examples of this type of puzzle. Furthermore, problems in which a number of pieces have to be arranged so as to fit into a (seemingly too small) box are also classed in this category. Computers aid in the design of new puzzles. A computer allows an exhaustive search for solution – with its help a puzzle may be designed in such a way that it has the fewest possible solutions, or a solution requiring the most steps possible. The consequence is that solving the puzzle can be very difficult. The two puzzles shown in the picture are especially good for social gatherings, since they appear to be very easily taken apart, but in reality many people cannot solve this puzzle. The problem here lies in the shape of the interlocking pieces – the mating surfaces are tapered, and thus can only be removed in one direction. However, each piece has two oppositely sloping tapers mating with the two adjoining pieces so that the piece cannot be removed in either direction. In an interlocking puzzle, one or more pieces hold the rest together, or the pieces are mutually self-sustaining. The aim is to completely disassemble and then reassemble the puzzle. Both assembly and disassembly can be difficult – contrary to assembly puzzles, these puzzles usually do not just fall apart easily. The level of difficulty is usually assessed in terms of the number of moves required to remove the first piece from the initial puzzle. Later puzzles introduced elements of rotation. At the beginning of the 19th century the Japanese took over the market for these puzzles. They developed a multitude of games in all kinds of different shapes – animals, houses and other objects – whereas the development in the western world revolved mainly around geometrical shapes. Stewart Coffin has been creating puzzles based upon the rhombic dodecahedron since the 1960s. These made use of strips with either six or three edges. These kinds of puzzles often have extremely irregular components, which come together in a regular shape only at the very last step. Furthermore, the 60Ŕ angles allow designs in which several objects have to be moved at the same time. The "Rosebud" puzzle is a prime example of this: in this puzzle 6 pieces have to be moved from one extreme position, in which they are only touching at the corners, to the center of the completed object. Vexiers are a different sort of disentanglement puzzle – two or more metal wires, which have been intertwined, are to be untangled. They, too, spread with the general puzzle craze at the end of the 19th century. A large number of the Vexiers still available today originate in this period. The aim in this particular genre of puzzles is to fold a printed piece of paper in such a way as to obtain a target picture. In principle, Rubik's Magic could be counted in this category. A better example is shown in the picture. The task is to fold the square piece of paper so that the four squares with the numbers lie next to each other without any gaps and form a square. Impossible objects are objects which at first sight do not seem possible. The most well known impossible object is the ship in a bottle. The goal is to discover how these objects are made. Another well known puzzle is one consisting of a cube made of two pieces interlocked in four places by seemingly inseparable links. The solutions to these are to be found in different places. There are all kinds of objects which fit this description – "impossible bottles" which contain objects that are far too large, Japanese hole coins with wooden arrows and rings through them, wooden spheres in a wooden frame with far too small openings and many more.

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