It's in a textbook or two, even in English, I'll hand that to you. But I think this makes a good case study in just how much can be considered "fundamental."
I did a Kombilo search on this position from Winter 2015 GoGoD, 85931 games total. Only 2554 of them, or about 3%, even contain this extension. So we are already looking at a position that only occurs in 3% of games even before the white play. Is this fundamental? I guess it depends on your viewpoint.
with black to play next appears in 46 games, or about 0.05% of the total games. (Actually 'a' and 'b' and more common than
, but one has to look at the whole board context in these situations in order to determine whether those moves would be called reductions.)I've seen the openings of maybe 2-3 thousand games. I know this
is in Attack and Defense, but I don't recall seeing it ever. I either truly haven't seen it or don't recall or maybe I never hit on one of those 46 games. However, I have played it recently but I messed it up because of something that probably really is basic.I suspect a lot of pros would call this
a basic thing to know. If so, we have our work cut out for us.Edit: The attachment of
occurs 282 times if there is white stone at 'c', so that's quite a bit more common at 0.3% of games. At that level, I should have seen it played, but maybe I didn't think much about it. In GoGoD, if something appears in more than 100 games, I consider it potentially worth studying.