Sue de Coq

Level 11 · Red Belt

Strategy:

Almost Locked Sets

Requires:

Almost Locked Sets Locked Candidates

Overview

Sue de Coq uses cells at the intersection of a box and line, combined with companion sets in the line and box. When candidates partition correctly, multiple eliminations become possible.

How It Works

Find 2-3 cells at a box-line intersection containing N+2 candidates (forming an AALS).
Find a companion set in the same line outside the box.
Find another companion set in the same box outside the line.
If candidates partition between intersection and companions, eliminate from other cells.

Example

Starting position

Look for Sue de Coq.

Sudoku grid showing the initial puzzle state for Look for Sue de Coq.

1

Intersection of row 6 and box 5

Find the intersection of row 6 and box 5 (2 cells with 5 candidates).

Sudoku grid illustrating step 1: Intersection of row 6 and box 5 — Find the intersection of row 6 and box 5 (2 cells with 5 candidates).

2

Helper set r6c1+r6c9 in row 6

Find helper set r6c1+r6c9 in row 6 outside the box. This ALS uses only candidates from the intersection.

Sudoku grid illustrating step 2: Helper set r6c1+r6c9 in row 6 — Find helper set r6c1+r6c9 in row 6 outside the box. This ALS uses only candidates from the intersection.

3

Helper set r4c4 in box 5

Find helper set r4c4 in box 5 outside the row. Its candidates do not overlap the row helper.

Sudoku grid illustrating step 3: Helper set r4c4 in box 5 — Find helper set r4c4 in box 5 outside the row. Its candidates do not overlap the row helper.

4

Extras outside the claimed candidates

The intersection and helpers claim these candidates, so the listed extras are removal targets: r6c8, r4c5, r4c6 and r5c5.

Sudoku grid illustrating step 4: Extras outside the claimed candidates — The intersection and helpers claim these candidates, so the listed extras are removal targets: r6c8, r4c5, r4c6 and r5c5.

5

Remove the extra candidates

The intersection and helpers claim these candidates, so remove the listed extras: r6c8, r4c5, r4c6 and r5c5.

Sudoku grid illustrating step 5: Remove the extra candidates — The intersection and helpers claim these candidates, so remove the listed extras: r6c8, r4c5, r4c6 and r5c5.

6

Result

Result after applying the technique.

Sudoku grid showing the result after applying the technique

Tips & Patterns

Sue de Coq is elegant but rare.
The intersection cells must share candidates with both companions.
Eliminations can occur in both the line and the box outside the pattern.