Diabolical cube

The diabolical cube is a three-dimensional dissection puzzle made of six solid pieces, each a polycube built by joining unit cubes face to face, in sizes of two, three, four, five, six and seven cubes. The solver's task is to fit all six irregular pieces together into one solid three-by-three-by-three cube with no gaps, a goal that looks simple from the piece count alone but is made difficult by how few of the pieces have an easily read shape. The puzzle is documented as the oldest known puzzle of its specific type, first appearing in the 1893 book Puzzles Old and New by Professor Hoffmann, the pen name of Angelo Lewis. Treating mirror-image arrangements as distinct from their originals, the cube has thirteen separate valid solutions, and because every piece is flat rather than twisted, the mirror reflection of any one solution is itself guaranteed to be either the same solution again or another valid one. The diabolical cube is closely related to later six- and seven-piece cube dissection puzzles such as the Soma cube and the Slothouber-Graatsma puzzle.