When considering a CGT game like

X = { 0 , * | 0 }

I have two questions: Does this games X have a special name (or value) in CGT?

And is there a Go-position (in chilled Go) that is equivalent to game X?

And the same questions for a simular game like
Y = { 0 , * | * }

Oh yes, thank you! I somehow expected it would be something more complicated than an Up (+) Star and an Up. The nice thing about this is that I don't need an additional theory to cover it

While it is quite easy to verify these values by simply playing it out (with adding the reverse values), I wonder if there is a direct way to get to these values? Or do you have to try adding all kinds of different values until you find the one that results in a zero-position?

By reverse values I take it you mean the negatives of the values.

On Numbers and Games, Winning Ways, and Mathematical Go all address how to simplify games. You delete dominated options and reverse through reversible options. Sensei's Library explains that, too, but maybe not as well as the textbooks, as Sensei's Library is not aimed at mathematicians.

Yes, that's what I meant. Using the word "reverse" instead of "negativ" was a bad choice, because "reverse" already has another meaning in this domain.


I've read either "On numbers and Games" or "Winning Ways" some years ago, but I can't remember wich one it was. Probably this is a sign to (re)read them both one more time. Actually I believe I was only interested in the stuff about the (surreal) numbers at that time and I know about the Up, Down, Tiny, Miny stuff only from senseis library.
Because I don't have access to these books at the moment, I want to ask one more question.

For removing dominated options I only know that one can (and should) remove all options that are clearly worse than another one, like in {1,2|3} Black would never move to the 1, because 2 will be always better (or at lest equal) than 1 for black.

And under removing reversals I understand something like forcing black to continue, if after a black move followed by a white move, white can move from here to a better position for her than she could get from moving in the initial position. (probably an equal position could/should be used, too, to qualify a play as an reversal)

But I cannot see, how this helps in this case.


In Y={0,*|*} it's not clear wether 0 or STAR is better for black.

The best black play depends on if there is an additional STAR or not.

When I try to solve it with my 'own' knowlege, the only way I see is to consider both szenarios:

1) Y = {0,*|*} (black wins)

2) Y+* = {0,*|*} + * = {*,*+*|*+*} = {*,0|0} (=X) (first player wins)

Probably you already knew that {0,*|*} = {0|*}, but for me it looks a bit like
{0,*|*} = ??? = {0|*}.
So I'd like to ask you if you could write down just one more step inbetween?