Template
A template is a pattern which guarantees some kind of connection. There are several different (and sometimes overlapping) types:
The carrier of a template consists of all of those cells (occupied or empty) that are part of the template. Empty cells in a template's carrier are an important part of the template and must not be ignored: if any of these cells are occupied by the opponent, the template is typically no longer valid.
Overlapping templates
Two templates overlap if some empty cell belongs to both of their carriers. Care must be taken with overlapping templates: although each template may be valid individually, the overlapping templates may not form a valid connection as a whole. The simplest example is the following situation, called a U-turn:
Although 1 is connected to 2 via a valid bridge template, and 2 is connected to 3 via a valid bridge template, 1 is not connected to 3, because the bridges overlap at *. In fact, if Blue plays at *, Red cannot defend both bridges in a single move.
