Ian Butler wrote:
I figured he could live on the top side, and I just wanted a big wall in exchange. So maybe the top was not so terrible (except for some mistakes).
Indeed, from move 19 to 29 it was black who was giving a wonderful example of your title "Invasions - what not to do". Your position at 29 is considerably better than it was at 19, black's invasion helped you build a nice wall and fix your weaknesses for meagre territorial gain.
I hinted to identify your weaknesses, it's a good idea to do this when your opponent invades (and other times!) and make a list. So at move 19:
- white f17 to f14 is a 2 space jump, this isn't connected. One space jumps are usually hard to cut (e.g don't need to worry about o15, plus you have q14 for support), but a 2 space jump is thin so should set a little "warning, cut possible" light flashing in your brain. (In fact this thinness means e18 was an overplay but black let you get away with it, d18 block should have been around c13, your e18 should have been around d14 directly, but maybe you thought you could bully a weaker player). Black could play f16 g16 f15 g15 and then cut at g17 or g14. More stylish ways of cutting like f16 g16 g15 also possible.
- the top is open at o18, so black can jump in at n18 or m17 is sente to connect
- right white group is pretty healthy, but there is some weakness at p15, or black could get a peep at n15
- top left group is less healthy due to the thinness of 2 space jump, black could also play f15 to start chopping it up.
- neither group has 2 eyes, but no need to make them for a while.
- black g18 is threat to connect to corner so might be handy in making eyes on top, but white d19 likely a sente defence against that.
So when black invaded for 19 the above analysis is the sort of thing you should do before deciding how to continue (at least the first 2 points for a 10k). You then capped at 20, this is a fine move, attacks black whilst loosely connecting your 2 groups. But did you consider tenuki? When weak players play bad invasions in small areas of the board, it is often a powerful idea to just play somewhere else bigger (and it's funny and can give you a psychological advantage). How about an empty corner, maybe that's bigger than the cap? Let's say you play d4, and then black jumps at k14, and you play q4, do you feel sad he got to jump? I'd feel pretty happy to get the first move in 2 empty corners. What I would feel sad about is my 2 white groups being separated, so I like capping to connect them (attacking black is secondary).
For 21 black continued inside, as I'd expect a human kyu player to do, but tenuki was probably better. Your f16 answer was good, black just helped you fix that 2-space weakness I was banging on about. Remember to say "thank you" to black. Ditto for the following few exchanges, what a lovely wall. For move 30 there's a decision, do you play your move, which is nice to short black's liberties and reduce his eyespace (and make some for you, also if black descended at g18 it is sente to connect to corner, though your d19 can prevent that in sente), or o18 to disconnect there, or tenuki? All seem plausible to me, though something good about o18 is it disconnects the top right black corner so later s15 is maybe sente for you. If I was black for 31 though I would be sorely tempted to play o18 to connect and give up on the junk g17 stones.
k15 does hurt black's liberties, but also helps him as now you can't cut at h17. L16 is good. L17 is ok, but also think about tenuki. The k18 cut is a mistake though and a very important technique lesson: when you cut like this and the opponent captures they get eyes. So the principal is to cut the side you
don't want. Cutting on the inside here means black lives, and then you can capture the m17 stone in gote afterwards (if you didn't make the m19/n17 blunder). Is m17 big and worth spending gote on? A BIG NO. So cut the other side (m18): if black captures this then k18 and j17 captures black in shortage of liberties and is fairly large (but I still prefer an empty corner, so just play there instead of L17). If when you m18 black decides he doesn't want the inside group to die and connects at k18, then you can capture the outside stone with m16. And now the crucial point is black doesn't have as good eyeshape inside because you didn't give him a ponnuki. Does black need to spend a move to live? I leave this as a reading exercise (but with k18 first there is no reading exercise, it's super alive already). Scachus mentioned n18 or m16 later, I strongly prefer m16 for the better aji to the centre.
P.S. for move 20 my favourite move is b15 and d15 atari, this helps fix the 2-space thinness somewhat (black can't cut after f16/f15 combo because white can then capture them) in sente , then I might cap or play an empty corner.