reversible play - loss and gain
Discussion moved here from last section of One-Two-Three.
Charles In this example the point is that Black has gained nothing yet, if we're just talking endgame. Simply playing and isn't typically kikashi - effective forcing play - because White a is now better than it was before was played.
In fact that claim is in a state of tension with the sente gains nothing idea (which could be called a OneTwo concept).
- Bill: Which claim? - not only gains nothing for Black, it loses something.
Charles Then next we may have Black a - White b, a sente exchange. Out of the three statements
- the / exchange loses Black something
- the Black a- White b exchange gains nothing
- the to White b exchange of four plays gains nothing
at least one must be untrue, no? In the diagram it could be that this is a double sente (for all we know), but assuming it is really Black's (one-sided) sente to play here (we can add context to make that apparent) I'd say, of these statements, 1 and 3 are true, and 2 is false (that is not a sente-gains-nothing case). Bill, please give us your interpretation.
So 2) and 3) are false. Black a - White b gains more than - loses.
As for a case where Black a is sente, - may not be sente.
Here is a case that is plainly Black's sente.
, tenuki. at 1.
We make the usual assumptions that the corner is Black territory and to the right is White territory.
The sequence, - , - is the normal 3-point sente for Black. And after - , the local count remains the same.
Is the position worse for Black than the original? Yes, it is, but it is not a loss in terms of the saying, Sente gains nothing, which refers to the local count. It is worse for Black because White's reverse sente is larger than before.
Before, if , then - , to gain 3 points. Now, after - , if , is gote. White is 1 1/3 points better off now, on average. - raises the local temperature but leaves the count the same.
See Double Sente is Relative, example 1, for another related position.