Sue de Coq: partition a line-box intersection
Sue de Coq starts where a row or column intersects a box. The intersection candidates can be partitioned into one set in the box and another on the line.
Key idea
Those disjoint sets account for every intersection cell, so their digits can be removed from the rest of the box and line respectively.
See the move, step by step
Partition the intersection of row 8 and box 7.
Step 1 of 4
Inspect a crowded intersection
Focus on the two open cells where row 8 crosses box 7.
Step 2 of 4
Find two complementary sets
The intersection uses 2, 6, 7, and 9. R7C3 supplies the box set 6/7, while R8C6 supplies the row set 2/9.
Step 3 of 4
Clean each side of the partition
Remove 6/7 from other cells in box 7 and remove 2/9 from other cells in row 8.
Step 4 of 4
Preserve the exact partition
The intersection remains unresolved, but its four digits are now locked into the supporting sets.
Try it on today's puzzle
Count cells and distinct digits carefully. The box-only and line-only supporting sets must be disjoint and together account for the entire intersection.
Play today