FIFI25 vs. murasawa, October 2021

Game information

 * Size: 11x11
 * Red: FIFI25
 * Blue: murasawa
 * Result: 1-0 (Red won)
 * Comments: Eric Demer
 * Location: Board Game Arena, game

Coordinate Conversion
This game was played with BGA's old hex implementation, so its coordinates and board orientation are different from what's shown on this page. ​ I apply a small rotation to show move coordinates and positions on this page:

(11;11) -> a11 ​ ​ ​ ​ (1;11) -> a1 ​ ​ ​ ​ (1;1) -> k1 ​ ​ ​ ​ (11;1) -> k11

Moves and Comments
​

​

​

FIFI25 plays ​ 1. a11

murasawa does _not_ swap, and plays ​ 2. f6



​

​

3. e6 ​ ​ ​ ​ good ​ ​ This works with the swap piece, since normally play towards an obtuse corner would favor whoever is on the short diagonal, but a11 means it would favor Red here.

4. e4

5. g7 ​ ​ ​ ​ h7 would normally be better (joseki), but g7 is good here, since if Blue connects to the k-edge with ​ ​ 6. h5 ​, ​ ​ then ​ 7. g5 ​ works well with f6, due to the edge template that f5+g5 would form.

6. f5



7. h5 ​ ​ ​ ​ 8. h4

9. c4 ​ ​ ​ ​ good (joseki) ​ ​ Blue is fairly strong towards the a-edge, so Blue will probably connect a-edge. ​ That means Red will probably need to ladder along the 1-edge, and c4 will be quite helpful with such a ladder.

10. c3 ​ ​ joseki again

​

​

​

​

11. d3 ​ ​ 12. c5 ​ ​ ​ ​ ​ ​ This ends the joseki.

13. e5 ​ ​ This seemed fine to me until I saw Blue's response :-). ​ Due to that response, Red should've tried j3 instead. ​ (j3 would create a ladder along the 1-edge towards a1 and a ladder along the k-edge towards k11.)

14. e8 ​ ​ ​ ​ This wins for Blue, though Blue did _not_ keep the win: ​ ​ Due to c3, Blue can keep c5 connected _and_ serving as an escape for height-3 ladders (Red can't foil), so Blue connects to the a-edge via f5 or c9. ​ For the k-edge, h4 gives Blue either a height-2 ladder plus a switchback threat or a height-3 ladder, and either of those is enough to climb to e8.

15. j3



16. h3 ​ ​ This is locally good - Blue is being tidy before laddering along the k-edge - and keeps Blue's win, but was not necessary: ​ i4 wins more efficiently than h3.

17. f4 ​ ​ h3 reconnected Blue to the k-edge, and f4 threatens Blue's connection to the a-edge, so Blue should keep Blue's win by defending Blue's connection to the a-edge with c9.

18. j2 ​ ​ Instead, Blue wastes a substantial fraction of a move, since Blue was already connected to the k-edge. ​ (via j2 or a ladder from i3 that can climb to e8) ​ Now, not only am I no longer able to prove that Blue wins, but I in fact prefer Red.

19. b4

5 was better (minimaxing): ​ ​ ​ ​ It gives Red a ladder escape fork at b2, so the only advantage b4 might have over b5 is avoiding a potential peep at e2. ​ ​ However, that is almost-always much less important than the extra strength b5 gives along the a-edge. ​ ​ Furthermore, in this case, since Blue has e4 and e3,f2,g1,h1 are all empty, that peep provably achieves nothing: ​ Red can just answer with e2 with d2, and f2+g1 will still be red-captured.

However, even b5 is almost-certainly not enough here: ​ If Blue responds in the cell Blue plays for 22, then the situation becomes the same as just after Blue plays 22 in the game. ​ ​ I would've played b9 instead of either of ​ b4,b5, ​ due to Blue's strength towards the k-edge.

20. b3 ​ ​ If Blue was playing this as a timesuji, then I think Blue should've played g2 instead, so Blue would have more of them left. ​ Otherwise, this was bad because redD2 captures e1+d1, and thereby kills b3. ​ Red _might_ play b7 to try punishing b3, but I would probably instead neutralize b3 with a move near the a-edge.

​

​

​

​

21. g2 ​ ​ ​ ​ simple and fine, since this makes ​ 20. b3 ​ completely useless to Blue

22. d8 ​ ​ ​ ​ Very Good: ​ ​ Before I saw Blue play this, the position looked good for Red. ​ With this move, I am almost-certain that Blue wins. ​ (Blue does _not_ keep this almost-certain win.)

23. c8 ​ ​ ​ ​ Red's only chance ​ ​ c8 has a connection to the 1-edge, and c5 is an escape for ladders under c8, so the 1-edge direction is settled.

24. b9 ​ ​ ​ ​ blunder; now Red wins ​ ​ _Red_ keeps this win for the short rest of the game.

Blue needed to defend along the 11-edge, either immediately with b10 (simpler), or after threatening to cut through near the middle of the a-edge (b7 is faster).



25. c9 ​ ​ forced

26. d7 ​ ​ Blue has a height-4 ladder. ​ If Red just pushes, then Blue will connect to c5 which will then ladder to b9.

27. b7 ​ ​ ​ ​ Instead, Red yields, winning.

28. ​ Blue resigns ​ ​ ​ ​ b7 connects to the 1-edge via c6 or a6.

​

​

​

​



Against "O", "*" is the same defense as if a height-4 ladder is pushed too close to an a3 swap piece: ​ In that case, the attacker might be anticipating a foldback underneath, but if the defender yields just before the attacker's push makes a bridge to the swap piece, then instead the the original _defender_ gets a height-2 ladder.



If Red pushes with c3, then Blue gets a foldback underneath. ​ Red should instead yield with b3, so that instead _Red_ gets a ladder.



To avoid this, Blue should pivot sooner.