Eques and Knott are playing a game of standard 3x3 Noughts and Crosses. At no stage of the game has Eques threatened to complete a row of three on his very next turn.

Suddenly Knott realises he must lose. What is the position?

  • 1
    $\begingroup$ I assume Knott is to move? $\endgroup$
    – Glorfindel
    Jul 1, 2020 at 10:33
  • $\begingroup$ Correct. Actually I should have mentioned that in my question otherwise we can remove any cross from Stiv's solution and stipulate Eques to move, which would mean multiple solutions (ignoring rotation and reflection). $\endgroup$
    – happystar
    Jul 1, 2020 at 11:22
  • $\begingroup$ I suggest changing the word "must" to "will". "Must" implies that Knott will lose even if Eques plays irrationally. There is no solution for that puzzle. "Will" at least suggests that Eques plays rationally. $\endgroup$
    – pokep
    Jul 1, 2020 at 18:55

1 Answer 1


The position is as follows:

enter image description here

No two of Eques's counters occupy the same line of 3 (satisfying the never-threatening requirement), and no matter where Knott (O) places their next O, Eques (X) has a winning move whereby he sets himself up for two winning moves simultaneously - Knott is unable to block both on their next turn:

O goes centre left --> X goes bottom right;
O goes centre --> X blocks bottom left;
O goes bottom left --> X blocks centre;
O goes bottom right --> X goes centre left.

enter image description here

Assuming Eques plays optimally - and is actually trying his hardest to win - Knott must lose indeed!


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