Simba wrote:
Just got done playing my first ever 19x19 match against another human

. Was brave and joined a 24k player's game - was pleased with the result! Would appreciate any feedback or tips on how I can improve if you'd be so kind! I tried to play light moves that avoided overconcentration, whereas my opponent's stones seemed to be very overconcentrated. He also let me have some play towards the edges/corners at the start for free which was nice. In relation to that, as a general principle, should I play the 3-3 point in the corners where I have a 4-4 point to secure precise territory in the late game?
There is no simple rule about it. In general, protecting your 4-4 point can be a great move in the late game. The 3-3 point is a very slow way of doing so, and doesn't usually come up in strong games unless white has pushed in a bit.
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Since my opponent could still potentially invade there, I think? What stones do I need in place (alongside the 4-4 one) to make sure that my opponent can't successfully invade in the corner by playing at the 3-3 point? Having the 4-4, 3-4 and 4-3 stones is surely enough, but how about say, having the 4-4 and 3-4? Or 4-4 and 3-5?
In isolation, white cannot live in the corner if black has the 4-4 and 3-4 stones, but the corner isn't that big on its own as white can still approach and undercut it on one side.
The 4-4 and 3-5 is more common if you want to solely protect the corner, as (in isolation) the 3-3 invasion does not work any more. This is still quite a slow move, though sometimes seen and sometimes very good.
The 4-4 and 6-4 or 4-4 and 6-3 are probably the most common ways to continue locally. These both make kindso f corner shimari. White can still live in the corner in both cases, but (in isolation, i.e. no white stones nearby), the 4-4,6-3 shape forces white to take ko (I'll leave this as an exercise, there are chapters of books devoted to these shapes which I won't reproduce here. Sensei's Library probably has good stuff on them). In both cases, even if white lives, black is saying that he doesn't care if white invades and lives, because the thickness he will make will be overwhelming. This is the most efficient way to play, in general, rather than the slower way of just playing 4-4,5-3, because it is not so slow and does not have just one plan that can fail.
(EDIT: I see you took the 6-3 option in most corners in the game. These were all good moves, and good ways of helping the corner efficiently).
The 4-4,7-3 is similar to 4-4,6-4. White can live in the corner, but black becomes very thick (and white probably gets gote if black wants him to), so black can play a big move to make use of his wall.
Finally, the textbook way to play with 4-4 is not to play like this but instead to consider that the 4-4 supports long extensions. It works well with adjacent 10-4 points, for instance. Whilst you can play nearby like you suggest (and this is perfectly good and strong), you should never neglect the option of extending a long way and playing on a large scale. Conversely, if you have played 4-3 in the corner, it is good to finish this off with 3-5, because the corner is 'unfinished' in a way that the 4-4 is not.
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Thanks very much, feedback is much appreciated! Also, could anyone give me a rough idea of what kyu level they think I played at? I thought I was around 25-28k before this game, but maybe not, I don't know.
It is almost impossible to judge kyu level (arguably it isn't even well defined) below 20kish. I can say that you very much outplayed him, though, perhaps they are a complete beginner.
I will say one thing on the game, continuing the topic of how to protect the 4-4 corner. At move 23, you play M17. Now you have two extensions from the Q16 corner, which is great. However, after playing R14, white's 3-3 invasion stopped working (or, white would get ko if black played right). After M17, which is quite far away, white would get...still ko! So the M17 stone helps your moyo plan, but it is not very efficient at helping the corner. For this reason, we often consider shapes like this to be bad - if white invades teh corner and lives now, hte M17 stone did not help and is now too close to black's wall.
Instead, this is a good time to play the P17 shape. These 3 stones very nicely protect the corner fully, and black has good territory as well as influence prospects. Alternatively, K16 would be a great move, which doesn't pretend to protect the corners but instead would make a massive moyo if white invades either one.