 Complete the following phrase:  As an illustration, the greatest handicap normally given to a weaker opponent is 9 stones. It was not until August 2008 that a computer won a game against a professional level player at this handicap. It was the Mogo program, which scored this first victory in an exhibition game played during the US Go Congress. By 2013, a win at the professional level of play was accomplished with a four-stone advantage. In October 2015, Google DeepMinds program AlphaGo beat Fan Hui, the European Go champion and a 2 dan out of 9 dan possible professional, five times out of five with no handicap on a full size 19×19 board. AlphaGo used a fundamentally different paradigm than earlier Go programs; it included very little direct instruction, and mostly used deep learning where AlphaGo played itself in hundreds of millions of games such that it could measure positions more intuitively. In March 2016, Google next challenged Lee Sedol, a 9 dan considered the top player in the world in the early 21st century, to a 