Double Series of Isols

Abstract

It is assumed that the reader is familiar with the following notions: regressive function, regressive set, regressive isol, infinite series of isols, the minimum of two regressive isols, combinatorial function, and canonical extension. We shall use the slightly more general definition of a regressive function introduced in (3). The next three notions are defined in (2), the fifth in (3), and the last two in (7 and 8).