Life In 19x19

How to answer the unsupported 4-2 submarine invasion?

Consider the large keima.

possible continuation:

Black's submarine seems kind of early to me, and the direction of white's shimari is odd too. The idea of playing from the outside with small knight move when your opponent plays 2-4 in inappropriate situations is something I was aware of before bots, but you probably don't see it so much in pro games (most common probably bump to keep corner) because they don't play the 2-4 in inappropriate situations so much (though probably more than we thought). What about if the submarine is played in more typical positions it is used? Also see similar idea from AG http://www.alphago-games.com/view/event ... 12/move/34.

Here's a pro game (black Ke Jie vs Zho Ruiyang) with a more typical usage. http://ps.waltheri.net/database/game/74620/. It's from 2016 and has the AlphaGo vs Lee Sedol game 5 opening which was popular back then but now seems so old fashioned! (small shimari, no 3-3 invasions). Black has the distant stone on the left side to support the submarine. Zhou played the classic bump to keep the corner, LZ #157 doesn't think it's so bad, just -1%, but on this position likes to take the outside with the small knight move. LZ thiks the submarine was the worst move of the game so far at -3.6% and preferred knight approach or a move on the top side.

Today, I applied the OP move to win a qualification tournament, thanks! :)

Sometimes white will try this (suboptimal) move:

Click Here To Show Diagram Code

[go]$$B
$$ ----------------------+
$$ . . . . . . . . . . . |
$$ . . . . . . . O . . . |
$$ . . . . X . . . . . . |
$$ . , . . . . W X . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . , . . . . . , . . . |
$$ . . . . . . . . . . . |[/go]

Possible continuations:

good for black:

Click Here To Show Diagram Code

[go]$$B
$$ ----------------------+
$$ . . . . . . . . . . . |
$$ . . . . . . . O . . . |
$$ . . . . X . 2 . . . . |
$$ . , . . . . O X . . . |
$$ . . . . . 3 1 . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . , . . . . . , . . . |
$$ . . . . . . . . . . . |[/go]

also possible (still not good for white):

(after black connects at a, white can play tenuki)

Click Here To Show Diagram Code

[go]$$B
$$ ----------------------+
$$ . . . . . . . . . . . |
$$ . . . . . . . O . 9 . |
$$ . . . . X . 3 . 7 8 . |
$$ . , . . . . O X 2 . . |
$$ . . . . . . 1 5 4 . . |
$$ . . . . . . . a X 6 . |
$$ . . . . . . . . 0 . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . , . . . . . , . . . |
$$ . . . . . . . . . . . |[/go]

Sometimes black can consider this:

Click Here To Show Diagram Code

[go]$$B
$$ ----------------------+
$$ . . . . . . . . . . . |
$$ . . . . . . . O 3 . . |
$$ . . a . X . 2 1 . . . |
$$ . , . . . . W X . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . , . . . . . , . . . |
$$ . . . . . . . . . . . |[/go]

Situational:

Blacks plays now at a!

Click Here To Show Diagram Code

[go]$$B
$$ ----------------------+
$$ . . . . . . . . . . . |
$$ . . . . . . 5 O . . . |
$$ . . . . X . 1 2 . 8 . |
$$ . , . . . 4 W X 6 0 . |
$$ . . . . . . 3 7 . 9 . |
$$ . . . . a . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . , . . . . . , . . . |
$$ . . . . . . . . . . . |[/go]

Gomoto wrote:Situational:

Blacks plays now at a!

$$B
$$ ----------------------+
$$ . . . . . . . . . . . |
$$ . . . . . . 5 O . . . |
$$ . . . . X . 1 2 . 8 . |
$$ . , . . . 4 W X 6 0 . |
$$ . . . . . . 3 7 . 9 . |
$$ . . . . a . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . , . . . . . , . . . |
$$ . . . . . . . . . . . |

Click Here To Show Diagram Code

[go]$$B
$$ ----------------------+
$$ . . . . . . . . . . . |
$$ . . . . . . 5 O . . . |
$$ . . . . X . 1 2 . 8 . |
$$ . , . . . 4 W X 6 0 . |
$$ . . . . . . 3 7 . 9 . |
$$ . . . . a . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . , . . . . . , . . . |
$$ . . . . . . . . . . . |[/go]

What situations?

@Bill: Sometimes this move is best, but the continuation is heavily depending on the surrounding.

possible continuations:

2 times application of the move. (Move 46 and 52)

Poor black did not know I had a look at the 4-2 submarine already