Wolfram's 2-state 3-symbol Turing machine
In his book A New Kind of Science, Stephen Wolfram described a universal 2-state 5-symbol Turing machine, and conjectured that a particular 2-state 3-symbol Turing machine (hereinafter (2,3) Turing machine) might be universal as well. On May 14, 2007, Wolfram announced a $25,000 prize to be won by the first person to prove or disprove the universality of the (2,3) Turing machine. On 24 October 2007, it was announced that the prize had been won by Alex Smith, a student in electronics and computing at the University of Birmingham, for his proof that it was universal. Since the proof applies to a non-standard Turing machine model which allows infinite, non-periodic initial configurations, it is categorized by some as "weak-universal". (Wikipedia).
