Is any initial combination of moves (the first 4 moves on each corner) completely valid (I mean, using only the 5 common moves), in the sense that it doesn’t give either player an advantage? For example, does it make sense that after two diagonal hoshis are played, one komoku is better than the other? Or would that only be true on smaller boards?
What I mean is that A would be better than B, since playing B favors White’s approach from the correct side. Is this something that matters on the 19x19 board or does the bigger size of the board make all of these just a minor irrelevant nuance and all the first corner combinations are fine?
No, how you play different first moves and josekis is important even on 19x19. That stage, called fuseki (the opening) is full of theories, direction of plays, and such…
There are a few consideration when playing a komoku (3-4) in front of a corner occupied by a hoshi (4-4) If he is on the same 4th line, white has a nice high approach move which works well with his hoshi. If you put it in the other direction on the third line then white has a bit less perspective on the side because that stone is sapping what could be built.
This specific point is the subject of the first chapter of “the direction of play” in which the author assumes and try to explain that move 2 lost the game.
Of course this is only main idea, you have to ponder other corners, pincers, and sente/tenuki on the whole board.
Yes, the direction choice of the initial corner moves can make a difference, but it is tiny in an objective sense (like 0.1 points difference from AI). It’s more relevant subjectively in leading to an opening that you are comfortable with and where you know the appropriate continuations and josekis. Kajiwara was massively exaggerating for effect.
For example having 2 3-4 points facing each other is considered advantageous for whoever has sente to approach the other because it combines an approach with big extension from yours. However, this advantage is not worth forsaking an initial corner move (see my Leela Zero Opening Gospel) so only applies on move 5 not move 4. Or to take your example, B is the “bad” direction (just considering the lower side) because it makes a white approach from the outside also an extension from White’s corner, but if white does that for move 4 it’s actually too early because black should take the empty corner which is bigger. So white should take the empty corner for move 4, and now black can repair that wrong direction by making a shimari, and now that shimari is facing black’s 4-4 and that’s (a tiny bit) better directionally than if it were the shimari starting with A facing the lower side! Interesting eh?
The full size board makes the direction interactions of adjacent corners smaller than on the small boards, but not zero. The interaction of diagonal corners is mostly around which ladders work, for example 4-4 vs 3-4 can make a critical difference to the small avalanche in opposite corner.
Wow, yes indeed that was interesting. Is it really bad if Black plays B and White does not take the corner and approaches B? Some moves that can follow after the approach: Black takes the corner and B gets surrounded; Black takes the corner and White approaches there too (or invades a hoshi); Black starts a joseki on the lower right corner which might give the corner to White after all, …
Failures in fuseki are about a very few points sometimes. It’s already very positive when we try to make sense in the directions and get a favorable result at the end. The advantage should matter much more at some pro level and even so, some top player like Cho Chikun were famous to not be so good in the fuseki (but much stronger in the subsequent moves of the middle game .
“Bad” in the sense of worse than optimal play according to AI and for reasons understandable by humans, then yes. But probably only - 0.2 points or so. It’s still perfectly playable if you want to and there can be a psychological aspect to these early approaches of white getting in black’s face and saying “Rawwwr, even though you play first I’m being active and annoying” that if they unsettle black can easily make up for the objective point loss.
Pros make this level of mistake too, particularly before AI: pretty much every standard opening before AI was a small mistake, such as Kobayashi, Chinese, mini Chinese, San ren sei.
Surrounded? A double approach hardly surrounds black, but initiates a fight which should be good for black when he simply runs out splitting white with the top right corner being black. A more sensible continuation for white after black ignoring the approach is to press, and we end up the below where black has a small advantage.
