Beginner Exercise 194 / Solution

Summary  

Let's summarize the situation first. Black x dies in gote while Black y starts a throw-in ko. On the other hand, White x starts the same ko and White y makes a seki. This strange kind of situation is called the "ten-thousand year ko".

Generally, it's wiser to play elsewhere because starting such a mutual throw-in ko makes the opponent take first and loses one extra point for the throw-in stone. Black should start the ko only when the ko threat situation is favorable and the gain is worth spending the move, that is in the endgame.

Black x in Summary  

Obviously, here is death in gote, since a White move at either a or b almost fills the Black group into a bulky five.

Black y in Summary  

Black can obtain life with points only via the ko fight, where White takes first. Black will get 9 points of territory by winning the ko. White can erase the ko possibility by making seki (White y).

White x in Summary  

On the other hand, White can kill Black only via the same ko. In this case, Black takes the ko first. White will get 19 points of territory by winning the ko. Therefore it's easier for White to start the ko while Black can't erase the ko possibility. He must just wait for White's decision - hence the name, "ten thousand year" ko.

White y in Summary  

White has the option of making seki with . Neither side gets points.