An unsupported play on the second line. Usually inside or on the edge of the opponent's framework. A supported play on the second line is a slide.
This is sometimes called a mole play (supposedly from the Japanese), and should not be confused with "subway go".
The hem play is like this:
On the edge of an open skirt, you see.
Submarine plays are usually trying first for quick life. Certainly they concede influence.
is the skirt approach. Black might also respond at a.
White plays this way, probably, to gain life in a black framework, avoiding the diagonal attachment. here won't kill the white group (the 3-3 point is still open), but is a good play for central influence.
Submarine plays accord with the current fashion for a sharp, territorial style (the 'Korean way').
If the game goes this way, White has managed something interesting by getting Black to answer the 3-3 invasion at , rather than .
emeraldemon: The following are pieces from QuickQuestions that I've ruthlessly ripped out of context and placed here for convenient perusal.
Kenn: This occurs a lot in handicap games between myself and dan players at my club, sometimes even as the opening move (as depicted). I am usually not sure what to do, and play a or b. Are these moves bad? What would be good?
Bill: Both are OK, as well as c - h. Ba is strong. It puts pressure on while strengthening . Also, it preserves symmetry.
In a teaching game, I like a. It shows spirit. I would also be impressed by tenuki. After all, the exchange, - , early on in the game favors Black.
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AlexWeldon: re: the 3-4 contact under hoshi Well, the contact move is a middlegame invasion joseki, like the 3-3 invasion or the submarine invasions at 2-4 or 2-5. It has more in common with these moves than it does with the keima approach, which is more of an opening joseki.
The difference between the contact move and san-san is that it aims more as settling on the edge than in the corner. San-san allows the opponent to choose the direction of play and is best used in situations where that isn't such an advantage. When one side is clearly worth more than the other, the contact move may be better as it allows the invader to choose the direction (since he will usually end up settling on the side on which he played the contact move).
The submarine invasions are similar to the contact move in that they have a definite directionality to them... when to choose the submarine and when to choose the contact move is a question I've never had a good answer to, so hopefully someone stronger than me can enlighten us both.
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