◇ Just read — no move needed
How a ladder works
A ladder is a chain of ataris that zig-zags to the edge: atari, the runner extends, atari again from the fresh side, extend, atari — each pair of moves leaves the runner on two liberties until the board itself closes the net. Its beauty is that the whole sequence is forced, so you can read it to the edge before committing a single stone. Two things decide whether it works: a friendly stone along the path tightens the chase, and an enemy stone anywhere on the path breaks it — which is why strong players glance down the whole diagonal corridor before starting. A broken ladder attempted anyway loses sente and donates the opponent a wall. The marked support here keeps the chase tight.