Hey there,

I (16k in OGS) often see as black that white takes the corner which is diagonal to my first corner. It's really seldom to see that white doesn't and then I will play diagonal. I am playing this just for fun and because it seems to be unorthodox. But why is it unorthodox?

Probably the biggest reason is that you can avoid a diagonal opening as either black or white, so if you never play it it's one fewer thing to study.

Some people also feel that a diagonal opening is likely to lead to more fighting and smaller territories, so it may favor white as komi represents a larger percentage of the final score. This is not likely to make any difference in most amateur games, though, and diagonal openings are still played occasionally in professional matches so likely aren't too bad.

If the first four plays are each in an empty corner, then each player can guarantee a parallel opening (one where each player has played in adjacent corners). White can do so by playing in the diagonal corner to and Black can do so by playing in an adjacent corner to . That being the case, if indeed best play is to play the first four plays in an empty corner, then making a parallel opening cannot be bad. Playing a diagonal opening may be better for Black if White allows it, but we do not know that. A parallel opening at least preserves equity.

OC, it is not a given that playing the first four plays in open corners is best. Go allows many possibilities. Diagonal openings may be less frequent than parallel openings, but they are hardly unorthodox. If you want to play one, feel free.

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A diagonal fuseki is, in a way, a large scale crosscut, thus the feeling that it encourages more fighting.

I didn't know that.

Isn't it more a question of how early in the game fighting begins?
My feeling says that if white plays a parallel opening, black will have the choice of going to either an parallel/nearest corner or to the diagonal corner. If black diagonal, there are 2 crosscuts diagonal over the board, indicating perhaps even more intense close fighting. But if black would choose parallel for move 3, it will more likely develop into 1 large front towards each other?

Either way, there will be some kind of fighting, sooner or later.

My understanding, now supported by Alphago openings is that W wants the right to play a good direction of 3-4 if the opponent plays 3-4. Therefore if B opens immediately with 3-4, this shows his hand and gives W a good point to take. And if b opens 4-4 (like alphago) then W prefers to wait by taking an adjacent corner so he can play 3-4 if B continues with a 3-4 expansion opening like the mini Chinese.

Things are more confusing with the 5-3 etc where according to alphago you should try to get your opponent to protect rather than aiming to invade etc. But I think pros used to disagree.

On the other hand the difference is too miniscule even for pros. But yes there is a logic to it.

Edit: I misread the question. I am explaining why W normally doesnt play diagonal to B's first move in professional games, not why the crossfuseki is rare.

Why is the cross fuseki rare: as B has to pay for komi. And we believe the advantage B has with the first move is to play fast and dominate the board with a tendency towards moyo. It is thought that cross fuseki is too balanced and symmetrical, not a moyo. But I have strong doubts. Cross-fuseki is fast, and may work well with tengen as supposedly alphago showed vs deepzen.

Indeed!

As White, I almost always offer Black the option of a cross game, just because I like them. I'm not strong enough to take advantage of the heavier komi (at least not consciously) but there's something enjoyable about digging in, claiming what territory is available and then butting heads early. If Go is a conversation or a negotiation, I feel like the cross game is getting down to brass tacks.

On the other hand, I feel less happy watching Black build a big one-sided moyo that I'll be a move behind, so offering him/her something else interesting to do seems good. Often Black agrees

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Would you or anyone be able to provide a game record of the alphago vs Deepzen? Or perhaps a link to a source that mentions the game? Thanks!!

I have also been wondering why pros don't play diagonal with white, as the 2nd move of the game.

I guess the only logical explanation is that a cross-diagonal opening is favorable for white, therefore black won't go for it; and then, it is more advantageous for white to not "show off his hands" and keep their choices open for the 4th move of the game, depending on how black played the 3rd move?

nope - that ain't it, 'cos it ain't, because by giving black sente, white is already 30 points down and komi's only 6.5 or somesuch.