Scan rows and columns together

Use one placement in several directions

A cat’s row and column are both full. Every other cell on those two lines can be excluded, even when it is far from the cat. That makes line scans different from the no-touch check, which affects only immediate neighbors.

Pick an unfilled row and inspect it from left to right. Ask which columns already contain cats, then which candidate regions are already filled, then which positions touch a cat. Repeat the process for an unfilled column.

Cross-check a promising region

Suppose a region spans two rows but one of those rows already has a cat elsewhere. All candidates in that row disappear from the region. You may now have a single candidate, or the remaining candidates may line up and create a region-line lock.

The specific board below records a real first forced step. Use the row and column labels in its diagram to reconstruct why other locations have disappeared. If a step follows earlier work, its preceding steps in the full walkthrough supply that context.

Keep a systematic order

Try rows first, columns second and regions third, then repeat after a placement. This is a way to organize attention, not a mathematical rule that rows must be solved first. A narrow region can be a better starting point when it immediately forces a cat.

A scan that finds no deduction is still useful: it shows which constraints have been checked. Avoid turning the absence of a single into permission to guess. Move on to candidate locks or read a staged hint.

A real step from gm-6-0001