186.

David Breyer Singmaster was born in USA in 1939. He is a retired professor of mathematics at London South Bank University, England, UK. A self-described metagrobologist, he is most famous for his solution and his huge personal collection of mechanical puzzles and books of brainteasers. He is also interested in the history of computers. The notation he gave is what is used now to describe the action in this game.

§ F (Front): the side currently facing the person

§ B (Back): the side opposite the front

§ U (Up): the side above or on top of the front side

§ D (Down): the side opposite the top,

§ L (Left): the side directly to the left of the front

§ R (Right): the side directly to the right of the front

§ ƒ (Front two layers): the side facing the person and the corresponding middle layer

§ b (Back two layers): the side opposite the front and the corresponding middle layer

§ u (Up two layers) : the top side and the corresponding middle layer

§ d (Down two layers) : the bottom layer and the corresponding middle layer

§ l (Left two layers) : the side to the left of the front and the corresponding middle layer

§ r (Right two layers) : the side to the right of the front and the corresponding middle layer

§ x (rotate): rotate on R

§ y (rotate): rotate on U

§ z (rotate): rotate on F

What game does this notation describe ?