# Morwen Thistlethwaite

 Morwen B. Thistlethwaite Background Information Alias(es): Country: United Kingdom Born: 1945 (age 73–74) Occupation(s): Mathematics professor Years Active: 1978-present WCA ID: [1] Claim to Fame: Thistlethwaite Algorithm

Morwen B. Thistlethwaite is a British professor of mathematics at the University of Tennessee, USA. From 1978 to 1987 he taught at the Polytechnic of the South Bank in London. During this period he shared an office with David Singmaster.[Singmaster p. 39]

## Thistlethwaite's algorithm

Thistlethwaite is famous for the Thistlethwaite Algorithm which allows a Rubik's Cube to be solved in a maximum of 52 moves. He devised this around July 1981. The method is too complex to be memorised by humans and so is only practical for computers. This algorithm is important from a theoretical standpoint however, as it was for a long time the method with the fewest number of moves.[2] The algorithm works by restricting the positions of the cubes into groups of cube positions that can be solved using a certain set of moves.[Singmaster p. 39]

## As inventor of the Petrus method

In the second edition of his Notes on Rubik's "Magic Cube" (October 1979) David Singmaster mentions that Thistlethwaite had invented a novel strategy for restoring the cube in a maximum of 85 moves. In the third edition (November 1979) Singmaster provides a description of the strategy:

Thistlethwaite's 85 move process involves first doing a 2x2x3 block, leaving say the F and R faces to do. He then correctly orients all the remaining edges (this requires U or D), then positions FU, FL, FD and then puts UFL and DFL correctly in place. He then does the R edges and the R corners in at most 13 and 10 moves respectively. The technique requires some look-ahead to make sure pieces will be in acceptable places at later stages. More importantly, he has found a repertoire of 3-cycles of corners on a face which do all the possible orientation changes while doing the 3-cycles and take at most 10 moves. He can also do all reorienting 3-cycles of edges on a face in at most 10 moves. [Singmaster p. 32-3]