QED Logic quod erat demonstrandum
Logic Ascent

How to solve this 6×6 logic puzzle

6×6 · steady · 12 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 934). Solving it from scratch takes 18 logical steps, using 6 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Shape squeeze, Forced chain. Every step below is forced: nothing here is a guess.

  1. First, every open cell left in this region sits in row 1, so its marker has to land there; that clears every other open cell in the row.
  2. Next, every remaining candidate in this region touches E2 and F2, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
  3. Then, every remaining candidate in this region touches B2 and B3, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
  4. After that, every remaining candidate in this region touches B5, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
  5. Now, if C2 were the marker, region 2 would end up with no open cell for its marker, which can't happen. So it can't go there.
  6. From there, 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.
  7. Following that, place a marker at B4. Region has exactly one open cell left. Placing here clears the rest of row 4, column B, and its region. Placing here also clears its 3 touching neighbours.
  8. First, place a marker at A2. Region has exactly one open cell left. Placing here clears the rest of row 2, column A, and its region.
  9. Next, place a marker at D3. Region has exactly one open cell left. Placing here clears the rest of row 3, column D, and its region.
  10. Then, place a marker at C6. Column 3 has exactly one open cell left. Placing here clears the rest of row 6, column C, and its region.
  11. After that, place a marker at F5. Region has exactly one open cell left. Placing here clears the rest of row 5, column F, and its region.
  12. Finally, place a marker at E1. Region has exactly one open cell left.

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