Baguenaudier
Baguenaudier, also known as the Chinese rings, Cardan's suspension, Cardano's rings, Devil's needle or five pillars puzzle, is a disentanglement puzzle featuring a loop which must be disentangled from a sequence of rings on interlinked pillars. The loop can be either string or a rigid structure.
It is thought to have been invented originally in China. The origins are obscure. The American ethnographer Stewart Culin related a tradition attributing the puzzle's invention to the 2nd/3rd century Chinese general Zhuge Liang. It was used by French peasants as a locking mechanism.
Variations of this include the Devil's staircase, Devil's Halo and the impossible staircase. Another similar puzzle is the Giant's causeway which uses a separate pillar with an embedded ring.
Mathematical solution
The 19th-century French mathematician Édouard Lucas, the inventor of the Tower of Hanoi puzzle, was known to have come up with an elegant solution which used Binary [numeral system|binary] and Gray codes, in the same way that his puzzle can be solved. The minimum number of moves to solve an n-ringed problem has been found to beFor other formulae, see.