# Lars Petrus

Lars Erik Petrus (born 4 November 1960 in Luleå in Sweden) is an accomplished speedcuber. He has been described as a Rubik's Cube icon and master.[1][2][3]

## Information

Petrus grew up in Gammelstaden just outside of Luleå.[4]

He took up speedcubing in the early 1980s, learning it over the course of a summer when he was unemployed.[5] In 1982, he became the national champion of Sweden, and went on to finish fourth overall at the first official Rubik's Cube World Championships held in Budapest, Hungary.[6][7]

He later published his method, known as the Petrus system, on the Internet. It became a fairly popular method among intermediate and upper-level speedcubers, although its more recent use has diminished considerably due to the increased predominance of methods such as ZZ, Roux, and CFOP. Petrus won the 3x3x3 Fewest Moves category at the 2005 World Championships held in November 2005 at Lake Buena Vista, Florida, USA claiming the US\$500 prize. He competed in the 2006 International Rubik's Cube Competition in San Francisco.[8] He currently (since 1995) resides in SF Bay Area, California, USA, where he works as a software developer.[5]

He has also catalogues and published an explanation of Ikea product names.[9]

## The Lars Petrus System

The Petrus System was designed as an alternative to the popular layer-based solutions of the early 1980s using 2v2v2 blocks.[10][1] Petrus reasoned that as a solver constructs layers, further organization of the cube's remaining pieces is restricted by what one has already done. In order for a layer-based solution to continue after the first layer had been constructed, the solved portion of the cube would have to be temporarily disassembled while the desired moves were made, then reassembled afterward. Petrus sought to get around this by solving the cube outwards from one corner, leaving him with unrestricted movement on several sides of the cube as he progressed. This method is often used to solve the cube in a fewest-moves solution.

### The method

The system uses seven basic steps to solve a Rubik's Cube.

1. Build a 2x2x2 block
2. Expand to a 2x2x3 without destroying the 2x2x2 block
3. Correct edge orientation (EO)
4. Solve two complete layers
5. Permute the remaining corners (CP)
6. Orient the remaining corners (CO)
7. Permute the final edges (EP)

Petrus invented three simple and flexible algorithms to complete the last three steps, which he named Niklas, Sune, and Allan.

While the method stands alone as an efficient system for solving the Rubik's Cube, many modifications have been made over the years to stay on the cutting edge of competitive speedcubing. Many more algorithms have been added to shave seconds off the solution time, and steps 5+6 or 6+7 are often combined depending on the problems each case presents.

## References

1. ^ a b Quenqua, Douglas (2012), "The Rise, Fall And Rise Of The Rubik's Cube", The New York Times, web, retrieved 13 March 2023
2. ^ Hartlaub, Peter (2003), Call it neo-Cubism: Not only is Rubik's little toy back, but nimble-fingered players can unscramble the puzzle in no time flat, web: SF Gate, retrieved 13 March 2023
3. ^ Quenqua, Douglas (2012), Rubik's Cube enjoying another turn in spotlight, web: Herald-Tribune, retrieved 13 March 2023
4. ^ Aftonbladet, 4 November 1981.
5. ^ a b Sundell, Camilla (11 April 2007). "Här klarar Smith kuben" [Here Smith manages the cube]. Aftonbladet (in Swedish).
6. ^ Andersson, Björn (18 August 2003). "Rubiks mästare" [Rubik's master]. Expressen (in Swedish). Retrieved 24 March 2023.
7. ^ Sheir, Rebecca (2017), The Rise, Fall And Rise Of The Rubik's Cube, web: Wburl, retrieved 13 March 2023
8. ^ Jardina, Elizabeth (2006), Area 'Gee' on a roll, web: Oakland Tribune, retrieved 13 March 2023
9. ^ Kajanus, Eliza (21 March 2018). "Snickra ihop ett Ikeanamn". Språktidningen (in Swedish). pp. 24–27.
10. ^ Lopes, Shawn (2006), Come on, let's twist again, web: Honolulu Star-Bulletin, retrieved 13 March 2023