Edge template IV2l

This page is about edge template IV2l (four two ell). There is also an edge template IV2i (four two eye).

The template:

(From: www.drking.org.uk)

Choosing which stone to connect

Red is guaranteed to be able to connect both of the two stones to the bottom, i.e., Red does not have to choose which of the two to connect (see below). But it is easier to analyze the template if we assume Red chooses one of the two stones to connect to the bottom. Here, we assume that Red wants to connect the stone on the right-hand side to the bottom.

Red has three threats. The first one uses bridges.

The second one uses template II-1-b.

The third one uses the ziggurat.

For a blocking attempt, Blue has to play on the only overlapping field:

Red 6 is connected to the bottom and can be connected to the top right by one of the fields marked with +.

Connecting both stones

To show that Red can, in fact, connect both stones to the bottom, we consider every possible intrusion into the template. Since the template is symmetric, we only need to consider intrusions by Blue into the right-hand side of the template (or on the center line).

If Blue plays in any of the cells marked "+", Red can respond at d3.

Then d1 is connected by edge template IV2d and f1 connects via e1 or e2 or edge template III2e. Since Blue has so far played only one of the cells marked "+", at least two of those three are still available. Also, since d3 captures c4 and d4, the overlap between edge template IV2d and edge template III2e does not matter.

If Blue plays d3 or d4, Red can respond at c3. d1 connects via two bridges, and f1 connects via e1 or e3. Since Blue has so far played only one of the cells marked "+", two of d3, d4, e4 are still available, which is sufficient to connect e3 to the edge.