Template VI1/Intrusion on the 3rd row

This article deals with a special case in the defense of edge template VI1a, namely the intrusion on the 3rd that is not eliminated by sub-templates threats.

Basic situation

In this situation, there are only 3 possible winning moves for Red, and they are "a", "b", and "c". Of these, "a" is the easiest to verify, so we will assume Red plays there.

Before continuing the analysis, we first note that Red can escape all 2nd row ladders coming from the left, as follows:

Apart from attacking the bridge, which Red defends, Blue's next move must be in the shaded blue area, or else Red plays at d and connects.

If Blue plays at c, e, h, j or k, Red responds at d and gets a 2nd row ladder, which connects. If Blue plays at b, Red plays at x and connects by edge template IV1a. If Blue plays at d, Red plays at x and gets a 2nd row ladder, which connects. This leaves a, f, g, i.

If Blue plays at a, f or g, then Red plays at b. Note that Red connect down from the left by playing d, and connect down from the right by playing y. The only way for Blue to block both is to play k, but Red with the same strategy on the left would at worst produce a 2nd row ladder toward the right.

Finally if Blue plays at i, then Red plays at d. Apart from the bridges, Blue is forced to play g, and then Red plays b, forcing Blue to block on the right part (against Red y), and then Red wins with z.

If Blue intrudes at a, then Red responds at b, forcing Blue to block on the right part, and then Red wins with j.

If Blue intrudes at b, then Red responds at a. Blue is still forced to play g, and then Red wins with z.