Minimal and irreducible links in the Shannon game

Abstract

We discuss weak and strong links (`virtual connections') in the Shannon game. General properties of these links are discussed, leading to a method to find all links of given size by a suitably pruned exhaustive search. This is applied to links on graphs of up to 11 vertices. We discuss the concept of reducibility of such links. Three simple reductions are considered, including one, the `short-cut', not previously described. The complete sets of irreducible weak links on up to 11 vertices and strong links on up to 10 vertices are presented. Some applications to the analysis of Hex are noted.