In fact, this proverb should probably read
Why this knight's move played? Probably because it is a double purpose move. Its first purpose is to make territory while connecting, ...
tderz White often has to continue to make shape with sabaki a and c if Black hanes at b. A different fight starts if black hanes at d. (see somwhere appropriate pages on Senseis and link it).
... and its second to prepare an attack like in this diagram. For comparison ...
If Black defends and connects at , he has no severe follow up so that White can ignore it and treat
as a forcing move.
This situation yields quite a different shape. In this case, an extension to is better. It prepares an attack at
.
tderz: the efficient peep in the previous diagram is the reason why White must defend at
. Otherwise she should not play
in the first place (and keep other options open).
tderz Because white is safe on the outside now, and Black has a 4-4 on the top left, it's time to exploit the weakness of the 4-4 and enter at san-san .
The difference of 4-4 on top left or some 3-4 might influence whether White jumps out at
in the first place.
This shows that a standard quite, honte move ( in previous diagram) can be sente.
Because the stones are one line higher, the keima has a weakness and does not cooperate too well with the follow up at .
tderz By exploiting the liberty problems of the marked black stones with a and b, White can capture it. (How can one show the edge of the board?)
This way, Black cannot avoid that the marked cutting stone will be captured. Usually he cannot avoid it in other variants either, e.g. with at a or b. (which always must be checked , of course)
I open up this proverb page as food for discussion. I have far from the theoretical background to back up these ideas but I do have the advice from Guo Juan and indeed experienced the strengths and weaknesses of the shapes discussed.
(later) I now realize that the answer may depend more of the surrounding stones than the line of the capped stone. See tower peep.
Could these two proverbs summarized as:
Reply to a capping play with a one space jump to the 4th line.
Charles Matthews This is one case where database search does seem to support the proverb(s).
I did a search for a region like this (marked points included), not anchored (so in any position along the side), and symmetrised for left-right reflection. Mostly this formation will arise as White capping Black's stone. The most common answer was Black at a (30%); then Black at b (15%), Black at c (13%), tenuki and White plays d (10%), Black plays e (8%).
In handicap go the answer at a is recommended, and it is also the common play in simple cases like this:
Black does usually react with or the marked point.
Bill: Of course, this is an artificial position, as the right corner is open.
Still, playing leaves Black a bit overconcentrated in relation to the left corner.
Charles Something to that.
This is from a pro game. now opens up the position in a way Black at a wouldn't. For example Black can attack at b.
Looking at how the cap is handled in pro games, one sees tenuki quite frequently as an answer. As one would expect, if there isn't a local response that is good-looking.
I'd like to know more about the contact play and tenuki answers:
taiji is the japanese for this keima ni boshi or boshi ni keima? :)
Alex Weldon: Boshi ni keima?, I believe.