Reverse Sente

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  Difficulty: Beginner   Keywords: EndGame

A reverse sente play is a play which forestalls a sente play of your opponent.

[Diagram]

Reverse sente

If Black were to let White play out this sequence (as shown in SenteGote), White would gain three points in sente. The value of the Black play is also 3 points, but in gote. However, since it forestalls a sente play by White, the actual value of the gote play is the same as a same-size sente play.

Thus, value of the play is the same as 3 points sente. [1]

Since gote plays only count half (see Basic Endgame Theory), this is equivalent to a 6-point gote play. So, Black should play this before he plays any 6-point gote plays.

-- MortenPahle

Comment: Usually White should play sente before the players get around to the 3-point gote (miai value). (A 6-point gote by deiri counting is a 3-point gote by miai counting. Confusing? Better stick to MiaiCounting.) Black gains the same amount on average by playing a 3-point reverse sente as a 3-point gote (miai values). Sometimes it is better to play one, sometimes the other, sometimes it does not matter. You can't make a hard and fast rule.

However, you should usually try to get tedomari. If you have a choice of gote vs. reverse sente that are worth the same (or often approximately the same), you usually want to get the last such play. Doing so depends on whether the number of gote is even or odd. (None are ko, which complicates things. ;-)) If the number of gote is even -- they are miai --, play the reverse sente to get tedomari. If the number of gote is odd, play one of them and answer the sente.

-- BillSpight


Charles Matthews One can get some feel from the stacks of coins model.

Given a chance of a reverse sente move you can play of value v, added onto a stacks position with largest stack s, there are just two ways the game goes. Either you reverse the sente and your opponent starts on the stacks: or you start the stacks, your opponent plays the sente v-point play, and then the stacks play out unaffected.

Here you are clearly faced with saving v at the cost of the advantage of starting the stacks. If that is guessed at s/2 we get the recipe 'double for reverse sente'. It could be as much as s, or smaller than s/2 in the presence of much miai: in which case the reverse sente is going to stand out as tedomari.


[1] NickGeorge Ok, If I understand reverse sente (which would be a bit of a shocker to me) it means the gote play prevents your opponent from making a sente play there. Thus, reverse sente > gote. But it seems I have to also say that sente > reverse sente > gote, because I can go from a sente play to a reverse sente play. Therefore, how can one say reverse sente value = sente value? Is it something like, it's gote, so half the value, but it prevents a sente play for an opponent, so double it again? I feel like you end up with something around 3/4.

Oh! I think I get it. You assess the value of all the moves and then go from highest sente down, and then any time you have sente go highest reverse sente down, and then highest gote down. But 7 points in gote > 3 points in reverse sente, so your reverse sente is not universally greater than gote.

Should I erase all this now that I understand? (if I do in fact understand)

Tirian: I don't think it's quite right to say that sente > reverse sente. Or perhaps it's just that "sente" might not mean what you think it would when there are reverse sente plays on the board.

I'm probably not good enough to get this right the first time, so hopefully some master player can see what I'm trying to say and correct the diagram if need be. In fact, the whole concept may be half-baked.

[Diagram]

7x7 endgame, Black to play

You might think to play the sente move at a before the reverse sente move at c, but when you play a you might find that White plays d instead and trumps your sente with a larger threat. If Black a, White d, Black b, then White plays e and you have lost more than you have gained. I think Black's only response is to finish the bottom edge allowing White to play b afterward.

Although I haven't seen it discussed outside CGT circles, I think that the value of a sente endgame move needs two values, the value of the sequence you expect to be played out, and the value of the follow-up move if the opponent plays elsewhere. Some moves are "more sente" than others even if they gain the same profit in the game.





NickGeorge:

[Diagram]

B: 11, W: 12

So this seems to me to be a "my sente's bigger than yours" deal.


[Diagram]

B:13, W:12

Black likes reverse sente, because the sente it prevents white from playing is bigger than the sente black could have played. Now I wonder, what if black had 2 sente moves, which combine to be greater than white's sente move.

I spent half an hour trying to make a diagram to demonstrate this, but failed. It seems, at any rate, that it would be possible to compile hard and fast rules for what order one should play these moves. Is this done anywhere?

Mef: Miai Counting gives a value for moves that takes into account sente values already, also most of the CGT pages deal with proper order of endgame moves. If all else fails you can play a difference game to give yourself a surefire answer.


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This is a copy of the living page "Reverse Sente" at Sensei's Library.
(OC) 2005 the Authors, published under the OpenContent License V1.0.
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