Isols and maximal intersecting classes

In transfinite arithmetic 2 n is defined as the cardinality of the family of all subsets of some set v with cardinality n. However, in the arithmetic of recursive equivalence types (RETs) 2 N is defined as the RET of the family of all finite subsets of some set v of nonnegative integers with RET N. Suppose v is a nonempty set. S is a class over v , if S consists of finite subsets of v and has v as its union. Such a class is an intersecting class (IC) over v , if every two members of S have a nonempty intersection. An IC over v is called a maximal IC (MIC), if it is not properly included in any IC over v. It is known and readily proved that every MIC over a finite set v of cardinality n ≥ 1 has cardinality 2 n ‐1 . In order to generalize this result we introduce the notion of an ω‐MIC over v. This is an effective analogue ot the notion of an MIC over v such that a class over a finite set v is an ω‐MIC iff it is an MIC. We then prove that every ω‐MIC over an isolated set v of RET N ≥ 1 has RET 2 N ‐1 . This is a generalization, for while there only are χ 0 finite sets, there are ϰ isolated sets, where c denotes the cardinality of the continuum, namely all the finite sets and the c immune sets. MSC: 03D50.