Sue de Coq

Level 9 · Purple 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

Look for Sue de Coq.

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

1

Sue de Coq

Find the intersection of column 3 and box 7 (2 cells with 4 candidates).

Sudoku grid illustrating step 1: Sue de Coq — Find the intersection of column 3 and box 7 (2 cells with 4 candidates).

2

Sue de Coq

Find helper set r1c3 in column 3 (outside box) - an ALS of 1-3 cells whose candidates are a subset of the intersection.

Sudoku grid illustrating step 2: Sue de Coq — Find helper set r1c3 in column 3 (outside box) - an ALS of 1-3 cells whose candidates are a subset of the intersection.

3

Sue de Coq

Find helper set r8c2 in box 7 (outside column) - an ALS with candidates disjoint from the column helper.

Sudoku grid illustrating step 3: Sue de Coq — Find helper set r8c2 in box 7 (outside column) - an ALS with candidates disjoint from the column helper.

4

Sue de Coq

Helpers claim all intersection candidates. Eliminate: r5c3 and r7c2.

Sudoku grid illustrating step 4: Sue de Coq — Helpers claim all intersection candidates. Eliminate: r5c3 and r7c2.

5

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.