Linking Sandwich Sets

Abstract

The theory presented in Chap. 2 gives precise criteria for the existence of sandwich pairs, but it does not provide a list of such pairs. There is good reason for this. The criterion

$$\displaystyle \sigma (1)\, A \cap B \ne \phi , \quad \forall \sigma \in \Sigma _Q $$

is very difficult to verify in practice, while the corresponding statement for linking pairs is easier. We were able to provide a reasonable list of linking sets at the end of Chap. 1, but we have not yet been able to do so for sandwich sets. In this chapter we shall focus our attention on this matter. It turns out that we can obtain a lot of help from the theory of linking sets.