User:Wurfmaul

A lemma (as seen on discord!)

A:

B:

From blue's perspective, A is at least as good as B.

Proof

When red plays first

The best red can do in A is to play at x, capturing the two cells below. When red plays at the empty cell in B, it kills the blue cell to the left of it, so the result is equivalent to the result in A.

When blue plays first

When blue plays at y in A, the result is at least as good for blue as when blue plays at the empty cell in B. To see this, note that if blue plays at x next, it kills z, and this implies that locally, red's only sensible move is at x, making the position identical to B.

reply by Demer:

That does not need the top red stone. ​ Also, it still works with a line of 3 red stones instead of the edge. ​ See automatic peep.