Defending against intrusions in template 1-IIIa

The edge template III-1-a
This template is also known under the name ziggurat.

R3 C4 Sa1 Sb1 Vc1 Sa2

Red has two main threats: R3 C4 Sa1 Sb1 Vc1 Sa2 Vb2 Pa3 Pb3 and

R3 C4 Sa1 Sb1 Vc1 Pd1 Sa2    Pc2 Vd2 Pc3 Pd3

These moves lead to easy direct connection. Because there is no common hex used in both threats, Blue cannot prevent Red to link to the bottom.