GridMewAn 8×8 walkthrough with upper and lower row locks
Follow original gm-8-0008 through a C reservation, a later F reservation and a separate shared-neighbor deduction.
On this page
Settle B, then reserve CApply two different arguments near FCheck the reasoning rather than the grid sizeApply the ideaCheck your understandingOriginal GridMew lesson · Updated 16 October 2026
Learning goal: Track two separate row reservations without mixing their regions or reasons.
Settle B, then reserve C
The givens at r1c5 and r5c1 leave B with r2c2. Once B is filled, every candidate in row 3 lies in C. That reserves C for row 3 and removes C’s row-4 alternatives.
Row 4 resolves at r4c3. Its column and regional effects help force r8c4, carrying the consequences of an upper-row reservation into the bottom of the grid. Keep updating the complete board instead of treating the two halves as independent puzzles.
Apply two different arguments near F
Later, row 6 can use r6c6, r6c7 or r6c8, all in F. The row reservation removes r7c8 from F. A separate touching argument removes r7c7 because that cell neighbors all three possible row-6 cats.
Those exclusions leave row 7 with r7c6. Placing it narrows row 6 to r6c8, which in turn settles row 3 at r3c7. The same row whose reservation started the upper chain is resolved near the end.
Check the reasoning rather than the grid size
This board has more cells to track than the compact examples, but the deductions still use one-cat quotas and immediate neighbors. No rule bans cats along a whole diagonal, and no two-star assumption is needed.
Use the diagrams below to audit each transition. If a proposed exclusion relies on a cat not yet placed or a candidate not yet removed, step back. A complete answer confirms the destination; the before-state explains how to reach it.
Apply the idea to gm-8-0008
r2c3 means row 2, column 3, counting from the top left.
The upper reservation uses row 3 and region C. The later one uses row 6 and region F. Keep their candidate lists separate: the reason a cell disappeared in the top half does not automatically apply to a similar-looking cell below.
At the lower checkpoint, the F reservation removes r7c8. A different argument removes r7c7: that cell touches all three row-6 candidates. Row 7 can then use r7c6. Naming those two reasons prevents a common shortcut that crosses out an entire neighboring row without proof.
How to approach this board
Coordinates such as r2c3 mean row 2, column 3. Count rows from the top and columns from the left.
The upper given reduces B to r2c2. After this single, row 3’s candidates all lie in C. Its reservation clears row 4, while a later reservation in F handles the lower-right corner.
8×8 · 2 fixed cats · 9 explained deductions. Region sizes: A: 6 · B: 4 · C: 13 · D: 21 · E: 5 · F: 6 · G: 5 · H: 4.
A deduction worth checking
At step 5, row 6 is confined to F at columns 6–8. That removes r7c8; the following shared-neighbor step removes r7c7.
A move to double-check · r7c8
Do not combine these two exclusions into one vague adjacency claim. r7c8 is removed by the F quota; r7c7 is removed by touching every row-6 candidate.
Green marks the cell being discussed, not a cat to place. This is the position before step 5; compare the deduction below.
Read the starting board as text
Each line is one row, left to right. Matching letters belong to the same connected region.
B B D D A A A A B B D C A A C C E D D C C C C C E D D C C C C C E E D D D D F F E D D D D F F F D D D D G G G F D D H H H H G G
Fixed cats: row 1, column 5; row 5, column 1. One cat is required in each row, column and region.
Step-by-step walkthrough
1Check region B
region B has only one remaining candidate: row 2, column 2. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 1. Place one cat, then exclude 7 other cells.2Use a candidate lock
Every candidate in row 3 lies in region C (row 3, column 4; row 3, column 6; row 3, column 7; row 3, column 8). Its cat must use that shared section. Exclude row 4, column 4; row 4, column 6; row 4, column 7; row 4, column 8 from the rest of region C.
Before step 2. Exclude 4 cells; then scan for a new single.3Check row 4
row 4 has only one remaining candidate: row 4, column 3. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 3. Place one cat, then exclude 6 other cells.4Check column 4
column 4 has only one remaining candidate: row 8, column 4. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 4. Place one cat, then exclude 3 other cells.5Use a candidate lock
Every candidate in row 6 lies in region F (row 6, column 6; row 6, column 7; row 6, column 8). Its cat must use that shared section. Exclude row 7, column 8 from the rest of region F.
Before step 5. Exclude 1 cells; then scan for a new single.6Exclude common neighbors
The cat in row 6 must occupy one of row 6, column 6; row 6, column 7; row 6, column 8. Each of row 7, column 7 touches every candidate, so none can hold a cat.
Before step 6. Exclude 1 cells; then scan for a new single.7Check row 7
row 7 has only one remaining candidate: row 7, column 6. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 7. Place one cat, then exclude 3 other cells.8Check row 6
row 6 has only one remaining candidate: row 6, column 8. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 8. Place one cat, then exclude 1 other cells.9Check row 3
row 3 has only one remaining candidate: row 3, column 7. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 9. Place one cat, then exclude 0 other cells.Show solution · reveals all cat positions
The final cats satisfy every row, column and region quota, with no edge or corner contact.
Cat positions: r1c5, r2c2, r3c7, r4c3, r5c1, r6c8, r7c6, r8c4.
Try another puzzle
Separate a regional reservation from a neighbor exclusion
gm-8-0012 · 8×8 · challenge
Practice candidate locks on another 8×8 board.
Read this walkthrough →A column reservation unlocks a small top region
gm-5-0012 · 5×5 · challenge
Transfer candidate locks to a 5×5 grid; compare how the candidates change.
Read this walkthrough →Successive column reservations cross the upper half
gm-8-0009 · 8×8 · challenge
Compare this route with shared-neighbor exclusions, and check why that different rule is needed.
Read this walkthrough →Check your understanding
Are r7c8 and r7c7 removed for the same reason?
Show the explanation
No. r7c8 loses F’s cat to row 6. r7c7 is a shared neighbor of every row-6 candidate. Both exclusions are valid, but their premises differ.