Larry D. Nichols Larry D. Nichols Larry D. Nichols, born 1939 in the United States, is a puzzle designer. He grew up in Xenia, Ohio, and studied chemistry at DePauw University in Greencastle, Indiana, before moving to Massachusetts to attend Harvard Graduate School. He is best known for the invention of mechanical puzzles including 'The Nichols Cube Puzzle' (1974), patent US365520. He has lived with his wife Karen in Arlington, Massachusetts since 1959. In 1957, 17 years before Dr. Rubik’s invention popularly known as the “Rubik's Cube”, Dr. Nichols conceived of a twist cube puzzle with six colored faces. It was a 2×2×2
Rush Hour (puzzle) has a solution is PSPACE-complete. This is proved by reducing a graph game called Nondeterministic Constraint Logic, which is known to be PSPACE-complete, to generalized Rush Hour positions. Tromp and Cilibrasi (2004) showed that "Rush Hour" is still PSPACE-complete when the cars are of size 2 only. They also conjectured that "Rush Hour" is still nontrivial when the cars are of size 1 only. Rush Hour (puzzle) Rush Hour is a sliding block puzzle invented by Nob Yoshigahara in the 1970s. It was first sold in the United States in 1996. It is now being manufactured by ThinkFun (formerly Binary