Difference between revisions of "Edge template"

Revision as of 17:58, 17 December 2020

An edge template is a minimal pattern that guarantees a virtual connection from a given stone, or sometimes several stones, to the edge.

Example

Here is an example of an edge template (template IIIa, also known as the ziggurat):

The red stone on the third row has a certain connection to the bottom, using only the hexes that are shown, even if Blue moves first. This is because Red is threatening either to play at "A" and connect via the shaded area

or to play at "B" and connect via the shaded area

Since these two escape routes for Red do not overlap at all, Red is guaranteed to be able to take one of them, no matter where Blue plays. Thus, Red is guaranteed a connection to the bottom edge.

Minimality

An edge template is by definition minimal. This means that every hex in it is essential to the template — in other words, if you remove any hex from the template then Red is no longer guaranteed a connection. For example, the ziggurat is a minimal edge template; if we remove any hex from the template, for example the hex marked "*"

then Red can no longer connect if Blue moves first in this area:

Blue has established a line across the bottom edge and clearly Red can no longer connect. There is no way through for Red, if Blue plays correctly.

Classification of edge templates

Main article: Naming of templates.

Edge templates are classified by how many stones the template contains, and how far the furthest of these stones is from the edge.

An edge template is a single stone template if it comprises only one stone. The ziggurat is an example of a single-stone edge template. There are many examples of edge templates that are not single-stone templates. For example the below pattern is a 3-stone template.

Red can connect their piece marked "↑" to the bottom edge, even if it is Blue's move. Here is an example of an attempt to block Red's connection by Blue, plus Red's route around the attempted block.

More edge templates

Many edge templates are known. Some are very important and show up in many games; others are so big and unwieldy that they are of essentially no practical use and are just of interest to people such as those analysing the mathematical theory of Hex.

Other template pages on this wiki:

• Edge templates everybody should know
• Edge templates with one stone
• Edge templates with two adjacent stones
• Edge templates with a bridge
• Ladder generation template
• Open problems about edge templates

See also

Unsurprisingly, edge templates play a very important role in hex. Players who want to learn more of the basics about edge templates should now read Edge templates everybody should know.

On a theoretical level edge templates are interesting too. Here are some open problems about edge templates.