His |17.u15 made it important to establish a connection to the right side. I could have delayed it with threats, but nothing that would help, as far as I could tell. So |18.s17 is the right move in this situation, because it has the lightest touch on the right side without actually letting him thru. This basically forced |19.r14, since it's the most threatening move linked to T13, and he needs that link, or the 20.s921.t10 threat comes alive again.
My next plan was to try to mix up the center, hopefully getting a peg with a strong enough connection to N13 that I could play p14 and make a double threat... I'm not sure how, but for example |23.q724.r1025.o826.p14. Unfortunately, his |23.t10 shut down the possibility. After my |26.u11, I hoped he'd be a little careless and play |27.o8, and then 28.p1429.p1530.r13. But he played it right, with |27.r9; I don't have enough threats to cross his parallelogram. I could threaten it with |28.p13, but that does me no good; in fact, it's easily answered: 29.p15. Game over.
His |17.u15 made it important to establish a connection to the right side. I could have delayed it with threats, but nothing that would help, as far as I could tell. So |18.s17 is the right move in this situation, because it has the lightest touch on the right side without actually letting him thru. This basically forced |19.r14, since it's the most threatening move linked to T13, and he needs that link, or the 20.s9 21.t10 threat comes alive again.
So after his |19.r14, I had a choice. This is probably the crucial move where I lost the game. I had originally thought that |20.m11 would be safe, but then I realized it was not really: 21.q16 22.p18 23.t19... or 21.q16 22.q18 23.o17 24.o19 25.m16. There are many alternatives, however, to |20.m11. Many choices. Maybe even one that works. Maybe |20.o19. But I wanted to preserve the connection to J10, and not have an uncertain battle across the bottom to the left. I thought |20.l14 covered my threats: |21.q16 22.q18 23.o17 24.o19 25.m16 26.l16 27.j13 28.j15 29.l12 30.h14 31.h12 32.f15.
What I completely missed was the threat of |21.q17. If |22.p16 then 23.s18 24.r15 25.u17 or 24.t19 25.p15 26.r20 27.p19. Crisis. I started to think things like |22.q20 23.r19 24.p18 25.t20 26.q16 27.v17 28.???, and |22.q21 23.s18 24.s20 25.n20 26.??? ... Argh, nothing works.
My next plan was to try to mix up the center, hopefully getting a peg with a strong enough connection to N13 that I could play p14 and make a double threat... I'm not sure how, but for example |23.q7 24.r10 25.o8 26.p14. Unfortunately, his |23.t10 shut down the possibility. After my |26.u11, I hoped he'd be a little careless and play |27.o8, and then 28.p14 29.p15 30.r13. But he played it right, with |27.r9; I don't have enough threats to cross his parallelogram. I could threaten it with |28.p13, but that does me no good; in fact, it's easily answered: 29.p15. Game over.