Ko fight example from a pro game - 9
This is the final game in the GS Caltex cup between Kim Jiseok (Black) and Lee Sedol. The ko fight starts at . The stakes of the ko cover the left to middle stones, including the chain at , affecting the lower left corner as well. The ko has been briefly analyzed at http://gogameguru.com/kim-jiseok-wins-18th-gs-caltex-cup/.
Black uses internal ko threats at and , while White threatens to revive his lost upper right corner.
Very soon, the upper right is exhausted and needs to start another ko as a threat to turn around the right side. This ko is huge as well. David Ormerod, 5d says in the above mentioned article at gogameguru that the left side is even larger.
The left side has become so large because Black has strengthened the outside while playing internal ko threats. here is another such move.
resolves the ko at the left side. When captures the ko at the right side, as an execution of the ko threat , Black immediately offers the exchange by strenghtening the outside of his left side. resolves the right side ko and - is an immediate reduction of its size, forcing White to play inside his freshly gained territory.
- is another such expense and then finally uses the sente Black gains from the ko fights.
This sente is a surprising feat: it was White who won the last ko (the one at the right side) and usually the player winning the ko gets sente as an extra reward. However, Black's last ko threat at was not really a threat, rather a fortification of his winning the ko at the left side. On the contrary, it was White who needed to execute his ko threat, by winnin the right side ko, allowing Black to take sente at the left.