The Journal of Symbolic Logic

Research Article

Variations on ◊

Keith J. Devlin

University of Lancaster, Lancaster LA1 4YL, England

Abstract

Various equivalents and weakenings of the combinatorial principle ◊ are considered. The paper contains both absolute results and consistency results. Also included is a new characterisation of the notion of a stationary subset of ω1.

(Received June 14 1977)