Two Button Go
Two Button Go is an amalgamation from two rules involving buttons:
- Button go, which makes area scoring rules as granular as territory scoring rules.
- Reverse Button Go, which removes pass fights from rules involving pass stones
Two button go involves two buttons, each of which has a value of 1/2 a point
The Combined rules are identical to AGA Rules, with the following changes:
- The game ends with 2 passes
- The first player to pass gets a button (normal button go)
- The last player to pass (ending the game) also gets a button. (reverse button go)
Since both buttons are worth 1/2 point, and both end up with one of the players, they either cancel out if both players got one of them, or they combine to give an extra point if a player got both of them. Because of this, two button go can also be rephrased as:
- If the same player gets the first and the last pass, that player gets an extra point.
The rules have the following advantages:
- Life and death can be determined by play, as under area scoring
- Counting can be done with the territory counting method
- The score is granular (common scores differ by 1 point, instead of 2 as in area scoring).
willemien thanks to Herman for updating this page. I only understood half of it.(or maybe even less) Still i have some questions. This differs from the description given at Button go where there is an unlimited supply of buttons (if i read a pm from bill correctly)
In short under AGA rules method, the player gives one pass stone to the opponent and gets a button in return (a 1/2 point "loss") , and the same applies to the last player. (it doesn't matter who makes the last pass)
Bill: Two button go does not promote early passes. Remember, it is used with territory scoring. Filling a dame gains 0 points, playing a button loses 1/2 point, passing loses 1 point. The normal progression is dame-button-pass (with the last button at the end).
Still wondering about some situations. what if one player can pass early but the game isn't over yet. For example see the problem on the left. (from the teire page.
If it is Blacks turn he can pass (and win the first button) but after white b he still needs to play teire at a. Is it fair that Black gets the button? especially because White has then lost the change to win it.
Bill: Not a problem. Compare these lines of play. 1) B button, Wb, Ba, W pass, B pass, W button. The buttons and passes cancel out. 2) Ba, Wb, B button, W pass, B pass, W button. All same same. :)
willemien : you are right. Thanks for the explanation.
wms: I'm very confused by this page. First, Bill's play series doesn't match the rules description at all; "B button, Wb, Ba, W pass, B pass, W button"? The rules say two passes ends the game and the player who makes the last pass gets the button, so black should get both buttons in that series. Similar problem in the second series. My understanding was that the first and and last players to pass don't GET the ½ point button, they GIVE the ½ point button to their opponent. Then the rules make sense I think.
Bill: (Later comment.) At the time I distinguished between taking the button and passing. I still do, but am willing to treat that as a separate issue. See implementation section below. :) One source of confusion is that sometimes the button is discussed from the viewpoint of area scoring, where taking it gains 1/2 point, and sometimes from the viewpoint of territory scoring, where taking it loses 1/2 point. The page could use some editing for consistency. :)
Herman: I think the confusion here stems from the fact that the pass stones are not explicitly mentioned. As said above, these rules are "identical to AGA rules" with some changes, so on a pass, you give a pass stone. That means taking a button wins ½ a point, but also loses a full point due to the pass stones. This is very close to your proposed "they GIVE the ½ point button", except it deals differently with intermediate passes.
So, in the example:
- B pass+button (W+½), Wb, Ba, W pass (B+1), B pass (W+½). Effectively, the buttons and pass stones cancel out.
- Ba, Wb, B pass+button (W+½), W pass+button(B+½). Again, the buttons and pass stones cancel out.
Bill, above, is considering a "button" as a move distinct from a pass, and lets the button be taken after two consecutive passes. In that case:
- B button (B+½), Wb, Ba, W pass (B+1), B pass (W+1), W button (W+½). Effectively neutral again.
- Ba, Wb, B button (B+½), W pass (B+1), B pass (W+1), W button (W+½). Effectively neutral as well.
Either way, the order of play in the example doesn't matter.
Implementation for territory scoring
Bill: Under territory scoring the two buttons are each worth -1/2 point. A pass costs 1 point. The first button, as with button go with area scoring, means that it normally does not matter who plays the last dame, unlike regular area scoring. The second button means that it does not matter who makes the last pass, unlike AGA scoring.
There is a simple way to implement double button go for territory scoring. Treat the buttons like passes. (Whether any pass lifts a ko or superko ban and how many passes end play can be treated separately.) The first player to pass hands over a pass stone, as usual. If the last player to pass is the same as the first player to pass, she does not hand over a pass stone for the last pass.
Why it works
A button may be implemented as a play in which one player hands over a stone as a prisoner but the other player does not. For instance, a play where Black hands over a pass stone but White does not is equivalent to a button with an original value of -1/2 point for Black. By taking the button Black loses another 1/2 point, for a result of -1 (equivalent to handing over a pass stone); by taking the button White loses 1/2 point for a result of 0 (equivalent to handing over no stone). The two buttons are then two plays, one in which Black hands over a pass stone, and one in which White hands over a pass stone. We simply require the first player to take the button to take the one in which she hands over a pass stone. Then if the same player takes the second button, it is the one in which she does not hand over a pass stone.
Note: AGA rules may be easily amended for double button go. Instead of requiring White to make the last pass, simply use the double button rule for the last pass. :) Territory counting would be used, OC.