That being said, the 3-3 invasion in the top right is still an option KataGo is considering early on here, and I don't think it'd be that bad to play it.
Agreed, but with one caveat. This is still just an unformed notion in my mind, but I think the word 'invasion' needs looking at again in the light of AI wisdom.
In military terms. invasion has strong associations with occupation, and I think, we carry that over to go. When we invade we look to live, and that further plays into the idea of living as big as possible. Obviously some invasions end in a running battle, but that's part of go being a two-person game, and equally obviously invading and living can sometimes be too small and so be the wrong strategy. But, on the whole, I'd say the ideal invasion involves occupying the opponent's putative territory with a healthy life. That in turn means we accept being attacked and surrounded, with the result that most such "good" invasions are gote.
But what I notice about AI play is that bots don't seem to make gote invasions, except in extremis. They will happily start sente invasions, but if things go pear-shaped they seem quick to abort, so as to keep the initiative. In my own mind I think of such bot play not as invasions but rather as 'raids'. In guerilla warfare is often a better model for go than regimental warfare.
This is not a new idea, at least for me. If you look at old Chinese games, invasions are relatively rare. The explanation is usually quite simple. Group tax applies. If you invade and live you are making a new, separate group, so there's -2 straightaway, and there's a strong chance the opponent, in enveloping you, will join two of his groups up, so there's another -2 points.
What you normally see instead is what I call 'encroachment' - a sort of mini-invasion or incursion (侵) where you make sure your encroaching forces stay firmly connected to friendly stones. And if possible you also try to drive in the wedge in such a way that you either split the enemy (分), or at least confirm his groups stay separated.
This is turn means that boundary plays have a much bigger profile in OC go, and explains why the Guanzi Pu (often incorrectly thought of as being a manual of endgame play) was such an important book - it was a novel manual of boundary plays. It does not feature many problems of the type you might expect if you have the word 'endgame' in your mind, i.e. those that have to do with making an extra point or so. But it does have a goodly number of relatively large-scale positions where the point is to make a mini-invasion or 'encroachment'. There are even encroachment josekis. Maybe the best known is the 3-6 Encroachment or 三六侵分, often played in the late opening even. 侵分 can be split up to mean 'intrude and separate' but is actually a single go word which was important enough to be taken over from Chinese to Japanese to mean 'yose' (i.e. boundary plays). It was common in Japan pre-war (rather than guanzi 官子), but usually required furigana to show the unexpected reading yose. That does not sit well with the modern temper, so we now get a simpler kanji or even just katakana.
All that is to make a case that 'invasions' can be and indeed have been re-thought in the evolution of go theory. So there is no reason why we should not ponder whether further re-thinking is necessary in the latest stage of evolution. Call them just sente invasions and gote invasions if you prefer, but in botdom I think it's important now to add the attributive.
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