QED Logic quod erat demonstrandum
Logic Ascent

How to solve this 6×6 logic puzzle

6×6 · steady · 13 steps

A
B
C
D
E
F
1
2
3
4
5
6
1
2
🐱
3
🐱
4
5
🐱
🐱
🐱
6
🐱

This 6×6 board rates as steady (difficulty score 817). Solving it from scratch takes 18 logical steps, using 6 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Paired regions, Shape squeeze. Every step below is forced: nothing here is a guess.

  1. First, every remaining candidate in this region touches E2, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
  2. Next, every open cell left in this region sits in row 3, so its marker has to land there; that clears every other open cell in the row.
  3. Then, together, two regions have open cells only in rows 1 and 2; with one marker each, those two markers have to fill exactly those two rows, so every other region's open cells there can be cleared.
  4. After that, every open cell left in this region sits in row 4, so its marker has to land there; that clears every other open cell in the row.
  5. Now, every open cell left in this region sits in column A, so its marker has to land there; that clears every other open cell in the column.
  6. From there, every remaining candidate in this region touches F2 and E4 and F4, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
  7. Following that, place a marker at D4. Region has exactly one open cell left. Placing here clears the rest of row 4, column D, and its region. Placing here also clears its 3 touching neighbours.
  8. First, place a marker at F3. Region has exactly one open cell left. Placing here clears the rest of row 3, column F, and its region.
  9. Next, place a marker at E1. Region has exactly one open cell left. Placing here clears the rest of row 1, column E, and its region.
  10. Then, every remaining candidate in this region touches B5 and B6, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
  11. After that, place a marker at C6. Region has exactly one open cell left. Placing here clears the rest of row 6, column C, and its region.
  12. Now, place a marker at B2. Region has exactly one open cell left.
  13. Finally, place a marker at A5. Region has exactly one open cell left.

The key move here was Shape squeeze. Once you can spot that, this board falls quickly. ∎