To understand the fascinating data sorin is showing (which in turn is part of our attempt to understand AI moves), we seem very much hampered by the traditional vocabulary.
Extension (hikari) is such a wishy-washy word. In the best-case scenario when one player has, say, a strong corner, 'extension' has a meaning we can relate to - moyo-building. In a slightly more complex fuseki, an extension may be designed to limit the opponent's expansion and we tend to recognise that by using a special term: a tsume or check, or checking extension. Using the same train of thought, we should perhaps be calling a hikari from a strong position an 'expansion' (which to me includes a 'swelling' nuamce). That is, we should be trying to convey its purpose rather than just describing its look.
The reason for making that observation is that the sorts of extensions in sorin's data are just extensions-by-look. The name tells us nothing about their purpose. It's too early for them to be moyo-building expansions or tsume moves. They are certainly not shimaris. What are they doing? I'm not really sure. The best I can come up with is a 'developing' move but even that is wishy-washy.
More important, a single word for all the types of extension shown here is unlikely to exist. A move like the centre play in a Chinese fuskei position or a sanrensei obviously has some element of connection with a stone in the other corner. Ideally that should be acknowledged with a word that means something like fuseki-connector. A move like a keima has a hugely different feel to it. In fact we tacitly recognise that already by sometimes calling it a shimari, but that is quite wrong. So we need a new word for that category, but what? Again I'm not sure myself. In this case that's mainly because I don't really understand what these keima moves are really trying to achieve. Yes, they have some element of protecting the corner, but - judging by old Chinese games where long extensions were quite rare and connected groups were a major goal - they are also seen by pros as moves with some connection impulse.
Any suggestions for what each kind of hitherto called extension is trying to achieve, and what we might call them to convey that? If we try to get away from the extension idea and call them 'marker posts' or some such word that a builder might use when laying out (which is what fuseki refers to) a building site, what are the posts marking and where do they point?
For reference, a shimari is a move that 'closes the door' and locks it shut, puts the bolt in, posts a Keep Out sign. Entry is only by housebreaking through a side window, not via a door and Welcome mat. It does
not leave the door ajar or on the sneck. It's not even strictly a 'corner enclosure'. The position in the upper left below is therefore not a shimari (shifted one line to the left, though, it would be). The triangled move below
is a shimari. This 'house' just happens to be a big one owned a rich person, but he still needs locks and bolts. This non-corner usage of shimari is explicitly mentioned by Hayashi Yutaka, but I have seen it myself (both on the sides and in the centre). So what do we say the upper left position is doing? It seems more like setting up an open cage as a trap than trying to seal off the corner. Can we see the notorious early 3-3 invasion as grabbing the bait before the trap is set? Has anyone noticed whether AIs play 3-3s once a trap is set? I haven't noticed any such behaviour.
Such a lot of questions to answer and so little time...
(;AB[dd][fc][dp][co][fp][jp][jq][pq][pp][on]AW[qq][qp][qn][qm]TR[jq]SZ[19])
When I was learning go those were the main shimaris for a 4-4 corner. The keima and iron pillar were sometimes used.
Playing through the variations indicates that the difference is not a typo. Did AlphaGo make a mistake when it played "b"?
