Senket — Puzzle of the Week #1 Solution

Update: Herman Hiddema came up with a much better solution.

This is the solution to the first puzzle of the week.

The territory is not secure, but only one invasion point will succeed.

Invasion at A becomes a prisoner immediately, while C, D, and E all fail with only a little struggle:

Red at A dies immediately.

Red at A dies immediately.

Red at C gets split. Whether Red plays above or below, Blue will take him prisoner.

Red at C gets split. Whether Red plays above or below, Blue will take him prisoner.

Red at D does no better.

Red at D does no better.

Red at E fails as well.

Red at E fails as well.

After Red at B, Red 3 guarantees territory.

After Red at B, Red 3 guarantees territory.

Playing Red 1 at B succeeds. If Blue plays at 2 in order to block Red from making territory immediately, Red 3 seals Blue’s fate. At that point, either F or G will form 2 points of territory for Red, and reduce Blue’s territory from 11 units to 2, for a total gain of 11 units. After Red 3, both players can look elsewhere, leaving the resolution here to the end of the game. Neither side has anything to gain by moving first.

Blue gains more territory locally by accepting his loss.

Blue gains more territory locally by accepting his loss.

Blue can gain an extra 2 units of territory locally by giving in to his circumstance. Blue 2 restricts Red to 1 point of territory and threatens to take 5 points back at 4. Red 3 cuts off Blue’s attempt to hold on to territory while threatening to take 2 points himself at 4. Blue 4 forces Red to settle for 1 point at 5. Blue can then take 3 points at 6. Even though the outcome scores better locally for Blue, this play is probably worse than the previous one because Blue leaves Red with the initiative. This previous play was 11 units for Red in Gote. This play is 9 units for Red in Sente, which is likely more valuable for Red and therefore worse for Blue.

In this scenario, if Blue doesn't manage to play at A then his posts are prisoners.

In this scenario, if Blue doesn't manage to play at A then his posts are prisoners.

To see why the final move is potentially so important, consider this board. If Red surrounds Blue and Blue neglects to play 6 at A, Red can do so instead. After that, Blue can’t form territory anymore, and has given Red 20 units of territory with 7 prisoners. Unlikely, but worth remembering. Try not to be so generous.

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4 thoughts on “Senket — Puzzle of the Week #1 Solution

  1. Pingback: Senket — Puzzle of the Week « Geoff Canyon’s Appeal to Authority

  2. Herman Hiddema

    Isn’t the “Blue gets more territory by accepting his loss.” line wrong? As I posted at the puzzle, isn’t 3-2, linking to 2-4 and 5-1 and immediately making territory, better? By immediately making some territory, blue isn’t forced to make move 6 in the last “scenario” diagram, and can thus take the initiative elsewhere, but also still has the option of 1-3 for even more territory…

    Reply
    1. gcanyon Post author

      I wasn’t clear enough. I’ve rewritten it to make all the “better for” references include “locally”

      But setting that aside, I think the answer you posted in your comment on the original post about blue at 3-1 is better still. It leaves blue with more territory and the initiative. I’ll work up a diagram later tonight if I can.

      Blue 1-3 doesn’t form any territory, so it doesn’t help him. (unless I’m misunderstanding?)

      Thanks for pointing this out.

      Reply
  3. Pingback: Senket — A Better Solution to Puzzle of the Week #1 « Geoff Canyon’s Appeal to Authority

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