How many people have seen or played games where they encounter the
"under the stones" pattern?

I don't think I ever encountered it in one of my games, but
a while back I saw a KGS game on youtube where it occurred.

https://www.youtube.com/watch?v=feXWiSgsyJ8

http://eidogo.com/#3ULavoL78

Do you mean the first joseki in the bottom left? If so, that is a very common and important joseki. If that is new to you, you should also understand how to respond if your opponent tries to hane and play C5 instead of D5. It's a notorious over play, but I have encountered even 5-6k players on KGS who make that move.

Not on the botton left, it's on the top left. It's where Black 121 captures back after being captured. I've never played an under-the-stones capture in any of my games, though I have done about a brazillion under-the-stones problems...

_________________
Patience, grasshopper.

I played an under the stones (the classic wriggly 4) as part of a team of 3 at the London Open rengo a few years ago. It was gratifying that we all (4d, 4d, 1k) saw it and rescued our group in an important fight. I don't remember playing it in a game of my own, though I have seen one in variations I've read a couple of times, and had them pointed out in reviews a few times too.

Edit. I did have the square 4 under the stones in the what looks like a false eye is actually a real eye shape on Tygem ages ago.

That's cool! Never seen that before. So, I've at least not seen it on KGS.

We need to consider that the rarity of seeing "under the stones" played out on the board is that there is a very narrow range of go playing ability where this would happen. Below that ability level (the ability to "see" an under the stones counter attack) neither player sees it so it doesn't happen. Above that ability level, both players see it, and the sequence leading to it is avoided. It is only when one player can it and the other can't that it would actually appear on the board.

How would white most likely have played if he had spotted the potential "under the stones" pattern early enough so he could still avoid it?

A recent pro game.

'under the stones' is quite common in life & death problems. In real pro games, it is not very rare either. For example, I saw this one recently when reviewing old games:



Actually, this is an interesting situation. Black B203 could avoid the 'under the stones', but he would then have to suffer from a loss in his territory due to short of liberties.

Isn't ko under the stones?

It can be.. like "sending two, returning one":

https://senseis.xmp.net/?SendingTwoReturningOne

https://senseis.xmp.net/?UnderTheStones

"A play under the stones (Japanese: ishi-no-shita) is a play in a space which has become free because some of your own stones have been captured."

But it depends how (super)ko is defined. Like whether you only consider the configuration of stones on the board or also take into
account which side is to move (regarding the question of whether a previous game state is repeated).

https://senseis.xmp.net/?PositionalVsSituationalSuperko

Insofar as this is meant to mirror the Japanese definition (e.g. as in Hayashi or the Nihon Ki-in terms dictionary) this is not quite right. They refer not a "play" (or a move) but to a "procedure" 手段. This word, which can also be rendered as "means", "expedient" etc has the nuance of resourcefulness - a bit extra than just a move. That is what I was trying to capture when I said there is an element of surprise involved.

It can be used in situations where a nakade is involved, but not the "humdrum" ones. Hayashi. for examples, mentions the case of a 30-stone nakade as an example of ishi-no-shita. He also gives a small nakade example where the "bulky" shape (horrible phrase - I prefer "clump" but it's not much better) is a bent four L-shape but on the side and the nakade is a placement in the middle of the long side of the L - again unusual.

He mentions these in the context of arguing for ishi-no-shita to be inclusive enough to encompass these examples in addition to the more traditional type where the move under the stones is a cut. In fact, ishi-no-shita is a relatively modern term coined for just that purpose. In old Japanese the term (obviously more restricted) was atogiri (after-cut).

Either way, simple things like kos, snapbacks, throw-ins and standard bulky/clump shapes are excluded.