hyperpape wrote:I think part of what's scary about mirror go to certain mindsets is that the recommendations about how to counter it are involve
1) taking a local loss, as in the case where you contact tengen, or
2) very abstract.
Maybe you're over thinking things a bit? It can be a little abstract, but nothing that's really any harder than many other aspects of go. When black mirrors, in particular, it's not that hard, because white probably has komi.
Go is all about trying to make your own stones work together efficiently and, conversely, trying to make your partner's moves become inefficient. Uberdude's game is an interesting example from that perspective. (Uberdude, I hope you don't mind some comments, I can see that you weren't taking the game particularly seriously)
The value of the tengen stone is important, so think about some ways that it can be used efficiently:
1. To attack. For example, to chase a group into the center and use it to block off the escape, or make things uncomfortable. In this way tengen can become a very effective move. This is often a good way to turn tengen into a good move in, say, a five stone handicap game too.
2. As a key stone in a large framework. This is harder to do well, but it also relates to the point above, because you never create a large framework expecting to keep all of it, but rather to pressure the other player into invading, so that you can attack and play actively while they have to defend passively.
3. As a 'universal' ladder breaker for all four corners. If you can play more severely in two or more corners, because of the latent possibility of a favorable ladder, you might be able to gain back more than the value of a move in those negotiations. Your stones should be working somewhat harder than your partner's in that case. Plus, tengen is still on the board
So, keeping those things in mind, have a look at Uberdude's game.
I don't know how to absolutely prove some of these things, but my feeling is that K3 is slightly bigger than K17, because black had more potential (with tengen) at the bottom than white had at the top.
Also, remember that black wants to use tengen primarily to gain an advantage through attacking, so allowing white O3 was questionable. I wouldn't have continued with the plan to mirror at all in this opening. I think black should play K17 at M3 instead.
O3 feels a bit bigger than F17 for the reasons already mentioned. White should be happy so far. I'd go so far as to say that white has a small advantage.
I felt that white R6 was questionable though, and P5 even more so. Remember that black wants to make sure that tengen remains an efficient move (as he does with all his stones) and make white's stones become inefficient. White wants to do the opposite.
A fighting game with running battles, or a center/moyo oriented game should be what black's looking for. A game with lots of small, settled territories - where the board is divided into small, localized struggles - should favor white. In an extreme case (hypothetical) where there were small territories all over the board and tengen became basically dame, white would win by komi.
Maybe this sounds too abstract? It's probably a bit unfamiliar because we're not used to dealing with tengen or mirror go, but it's something you can assess visually.
Look at the board after the exchange of R6 for C14. Two things have happened:
1. Black's gained potential on the left side which is enhanced by the tengen stone, while white's gained potential on the right which is reduced by the tengen stone.
2. The star point stones at Q4 and D16 have both lost their bases and are floating. A running battle in the center will be more favorable to black than white.
Continuing with the exchange of P5 and E15 compounded the problem. I think black was better at this stage. K3 has become a strange looking move, whereas K17 (while still strange) at least works with tengen to map out a large framework.
I can understand that these moves were motivated by fighting spirit, but the kosumi in the top left was a very big point. It would have been better if white had a stone at 6, but how about lightly erasing like this instead now?
In the diagram above (hidden to save space), if black pushes and cuts with a-c, white can play d to manage the situation. After d, x and y are miai. After black y, white x, the cutting stone at c can't be laddered (thanks tengen!) but if black tries to save the two stones at 6 and a, several moves like z will soon become double threats, because z (for example) also threatens to capture c in a net, starting with q. So black might play y at x instead, but then white will force with q and play y. The aji at B18 isn't an urgent problem for white and white can fix it with E18 later.
If white mirrors 7, there are a few possible moves, but settling in the top left with 8 seems good enough and better for white.
For similar reasons to those already mentioned, I think black should have stopped mirroring after white 14 (C6) and played the one space pincer at C8. O17 was alright for white, black F3 should still be the pincer (the bottom is small) and C3 seems better at R17. I won't do more diagrams because this is already a long post, but I hope you can grasp the feeling that the analysis doesn't have to be deep and complicated.
. I agree with what you said of going for the p5 e15 trade being good for black as not only do those moves create territory (well not quite as 3-3 still lives...) on the inside, but influence on the outside and suddenly that means that black's tengen stone can work towards centre points which I then needed to do something about with the L11 tactic.