QED Logic quod erat demonstrandum
Logic Ascent

How to solve this 8×8 logic puzzle

8×8 · gentle · 11 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 654). Solving it from scratch takes 23 logical steps, using 5 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Paired regions. Every step below is forced: nothing here is a guess.

  1. First, together, two regions have open cells only in rows 2 and 3; 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.
  2. Next, 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.
  3. Then, place a marker at H4. Region has exactly one open cell left. Placing here clears the rest of row 4, column H, and its region. Placing here also clears its 2 touching neighbours.
  4. After that, place a marker at E5. Region has exactly one open cell left. Placing here clears the rest of row 5, column E, and its region. Placing here also clears its 2 touching neighbours.
  5. Now, place a marker at G6. Region has exactly one open cell left. Placing here clears the rest of row 6, column G, and its region. Placing here also clears its 1 touching neighbour.
  6. From there, 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.
  7. Following that, 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. Placing here also clears its 1 touching neighbour.
  8. First, every open cell left in this region sits in row 7, so its marker has to land there; that clears every other open cell in the row.
  9. Next, place a marker at B8. Column 2 has exactly one open cell left. Placing here clears the rest of row 8, column B, and its region. Placing here also clears its 1 touching neighbour.
  10. Then, place a marker at D7. Region has exactly one open cell left. Placing here clears the rest of row 7, column D, and its region.
  11. Finally, place a marker at C1. Region has exactly one open cell left.

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