Alter Igo Endgame

3x4 Alter Igo example  

Black has played suboptimally, so now that it is his turn, he will lose.

3x4 example  

Black has to play somewhere, but any move on the right would be a single stone suicide, i.e. an immediate loss. captures 6 stones (5 black ones and the stone itself)

3x4 example, continued  

at , at

3x4 example, moves 9 and 10  

After this, black 11 must commit a two stone suicide at the marked point (which is ok) but then white will play move 12 at , leaving black no choice but to play a single stone suicide:

3x4 example, after 11 and 12  

Now black has no choice but to play a losing move.

Regular endgame

These positions might happen in a regular game of Alter Igo.

Common liberties

A play at a common liberty is worth a move. This is not a surprise, as the game (nearly) always ends with one of the players having to fill the eyes of their own (previously) living group.

Mirror game example  

In this 5x5 game, white has blindly mirrored black. This was not such a great idea.

Mirror game, black gets the last dame  

As there were an odd number of common liberties, black was able to play the final common liberty. White cannot play inside black's eyes (single stone suicide will lose immediately), so she must fill her own eye with .

The white stones will all get captured, and any further white stones will share that destiny. So, black will eventually be able to turn the whole board into one-space black eyes, thereby forcing white to play a "losing move".

Spare eyes

The player with more spare eyes will win.

Spare eyes example  

The player with more "spare eyes" will win. Here black has 1 spare eye, while white has none. (2 eyes are needed for living, as usual). The game will continue with white and black both playing inside the big white eye until it finally becomes a one space eye:

shrinking the eye  

is a two stone suicide, but that is quite okay by the rules. Continuing the game..

Black's spare eye wins  

Because black had an eye that was not needed for living, b was able to win by shrinking the white eyes to one-space eyes and then playing in the "spare eye".

Two-space eyes

A sacrifice inside a two-space eye is worth a move.

Two space eyes example  

In this position the black cannot fill his own 2-space eye, because white would mirror, forcing black to fill his own eye. Black can manage a draw, however.

Two space eyes: best play  

White also has to play inside black's two space eye, for if white uses to capture , black will play at and win.

Two space eyes: a loop  

Next, both players must commit two-stone suicides (confirm for yourself that any other move will lose), bringing the situation back to the original one 4 moves ago.

As neither player can deviate from the loop, after 4 further moves the original position will occur the third time, causing a draw.

Three-space eyes

A three-space eye is a slightly silly creature in Alter Igo. The opponent will of course take the middle point to prevent an extra eye. After that, you can use one move to turn it into a two space eye, or you can let the opponent play once more in the eye. If you do, you have "a move and an eye" in reserve: if your opponent is forced to play a suicide inside the 3-space eye, you will gain 2 small eyes, while it is still your opponent's turn to play next. Also, if you play to capture the two stones, you can "waste a move" and still have an eye left.

3-space eye example  

The player to play next will win this game.

This diagram could arise from "spare eyes example" if black made a mistake and played inside the white eye with . Notice how black's apparent spare eye advantage is of no use now!

3-space eye, white first  

has to remove a black spare eye or create a white one. In either case white will win.

3-space, white first, continued  

Black was forced to fill his own eyes first, so white won.

3-space eye, black first  

If it had been black to play first, white would have had to reduce her 3-space eye into a 2-space eye. Black would then have played inside the 2-space eye to win.

Exercises

While this page is not nearly complete, it should give some insight into the engame of Alter Igo. As there is very little other use for such wisdom, here are some endgame problems to test your skill. Have fun! --Bass, 2008-01-10