QED Logic quod erat demonstrandum
Logic Ascent

How to solve this 6×6 logic puzzle

6×6 · gentle · 11 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 gentle (difficulty score 773). Solving it from scratch takes 19 logical steps, using 6 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Line confinement, Shape squeeze. Every step below is forced: nothing here is a guess.

  1. First, place a marker at F1. Region has exactly one open cell left. Placing here clears the rest of row 1, column F, and its region. Placing here also clears its 1 touching neighbour.
  2. Next, every open cell left in this region sits in row 2, so its marker has to land there; that clears every other open cell in the row.
  3. Then, 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.
  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 in column A belongs to the same region, so that region's marker has to be somewhere in this column; that clears every other open cell in the region.
  6. From there, every remaining candidate in this region touches D3, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
  7. Following that, place a marker at E3. Region has exactly one open cell left. Placing here clears the rest of row 3, column E, and its region. Placing here also clears its 2 touching neighbours.
  8. First, place a marker at C2. Region has exactly one open cell left. Placing here clears the rest of row 2, column C, and its region.
  9. Next, 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 1 touching neighbour.
  10. Then, place a marker at A6. Region has exactly one open cell left. Placing here clears the rest of row 6, column A, and its region.
  11. Finally, place a marker at D5. Region has exactly one open cell left.

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