QED Logic quod erat demonstrandum
Logic Ascent

How to solve this 8×8 logic puzzle

8×8 · gentle · 12 steps

A
B
C
D
E
F
G
H
1
2
3
4
5
6
7
8
1
2🐱
3
4
🐱
5
6
🐱
🐱
7
🐱
8
🐱
🐱
🐱

This 8×8 board rates as gentle (difficulty score 765). Solving it from scratch takes 21 logical steps, using 5 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Shape squeeze. 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, place a marker at F2. Region has exactly one open cell left. Placing here clears the rest of row 2, column F, and its region. Placing here also clears its 3 touching neighbours.
  3. Then, place a marker at D1. Region has exactly one open cell left. Placing here clears the rest of row 1, column D, and its region.
  4. After that, place a marker at E4. Region has exactly one open cell left. Placing here clears the rest of row 4, column E, and its region.
  5. Now, 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.
  6. From there, place a marker at G5. Region has exactly one open cell left. Placing here clears the rest of row 5, column G, and its region. Placing here also clears its 1 touching neighbour.
  7. Following that, every open cell left in this region sits in column B, so its marker has to land there; that clears every other open cell in the column.
  8. First, place a marker at C3. Region has exactly one open cell left. Placing here clears the rest of row 3, column C, and its region.
  9. Next, every remaining candidate in this region touches A6 and A7, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
  10. Then, place a marker at A8. Region has exactly one open cell left. Placing here clears the rest of row 8, column A, and its region. Placing here also clears its 1 touching neighbour.
  11. After that, place a marker at B6. Region has exactly one open cell left.
  12. Finally, place a marker at H7. Region has exactly one open cell left.

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