In top players' games I've seen usually two approaches to 5-5 stone. When is it better to play A, and when to play B? What are other reasonable options?

Oh I doubt that we can reach any sort of agreement here between the top players.

First of all there are at least 3 other options -> c11, d10, d9. Possibly also b12, c8… In rare cases even b11.

Secondly, none of them is arguably any stronger than the others in an open board. It all depends on the global position.

Could you go into what features of the global position might influence the choice, Arek?

Also I assume your “other options” are in response to the equivalent white e9?

I've never put that to words so I think all that up all over again every game ;)

Basically with local play you always weaken one side in order to strengthen the other side (only if you do it correctly, otherwise one may lose on both sides)

So the principle is that you have to strengthen the side which is more important to you

Heh anyway black is winning here so white just gets to choose how to lose :-)

Force majure, the reasonable options are these: http://www.trmph.com/hex/board#13,i5j2a13j3b13j4b12k3a12

Basically white is trying to get some supporting stone on right side and/or trying to get some stone on top side.

h4 is also playable, I would say.

To answer the original question, I'd say that B is the better default option if you don't know what you're doing. It gets stronger if white has a ladder escape at the bottom right, and weaker if black has an escape at the top left. So for example, this is a pretty standard B selection. (Though obviously black is still winning given the initial stone.)

The time for A is a bit more rare. I like it when white has some escape power on the bottom right, but not *too* much. I think this opening looks reasonable, though maybe others disagree. It is also probably good when black has some, but not too much, strength at the top left. Here's another example.

If white has no strength on the right, j4 can be the better choice, e.g. this

Thanks for your opinions. Shalev: I understand the first paragraph, but I don't feel the second one, why you don't want too much strength? And how would you imagine to continue after playing the joseki in the last example?

For the last example, maybe something like this, with white going for an escape on the obtuse corner instead of the acute corner on the right hand side.

For option A (my second paragraph), the thing is that if white has a lot of strength on the bottom right and black has no strength on the top left, option B is better. So you're only even considering A either because 1. black's escape options on the top left are decent, or 2. your escape options on the bottom left aren't great. In the former case, you're afraid of a ladder on the top; this is bad for white. It's better to do this, giving white those nice support stones in the middle of black's territory. In the latter case, you're afraid of a ladder on the right; this is also probably bad for white, or at least giving black the option to do this is bad. (Laddering with no escape plan is generally not recommended.) This is much better.

Remember that it's black's choice whether to ladder on the right or on the top, so white wants to optimize for the worst case between the two. Black also has other, more complicated options, but those two ladders require a contingency plan on white's part, so they are usually the first thing I look for.

shalev, i also can't understand your explanation very much. To be honest it's almost impossible to explain hex in words because we lack a common vocabulary. Anyway i agree that h4 is also playable. I had left it out because I think it requires some support on top for white and so it's kind of a special case.

To be honest I think the best is just “tenuki”, play somewhere else. The fact that there are multiple choices usually means that we should not play there yet.

And I would say that the other corner is much more friendly to “josekis” because there are almost no choices at all.

Hmm, well, do people understand what I mean by “ladder” and “escape”? A ladder is this, and an escape lets you win the ladder. The c10 stone here is an escape for the ladder.

Generally, if you have a ladder escape and you're laddering on your side (like white in the above examples), then extending the ladder is good for you and bad for your opponent. If you have no escape plans at all, then extending the ladder is usually not good for you (it is more likely to be fine for lower ladders (those closer to the edge), like second row ladders, and less likely to be fine for higher up ladders, like fourth row ladders).

I found the clarification made sense

Shalev, I appreciate your time and work. Thanks!