In [2], Prikry showed that if κ is a weakly inaccessible cardinal which carries a Rowbottom filter, then there is a Boolean extension of V (the universe), having the same cardinals as V, in which cf(κ) = ω. In this note, we obtain necessary and sufficient conditions which a filter D on κ must possess in order that this may be done.

Various equivalents and weakenings of the combinatorial principle $\diamond$ 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 ω 1.

I argue that the role played by infons in the kind of mathematical theory of information being developed by several workers affiliated to CSLI is analogous to that of the various number systems in mathematics. In particular, I present a mathematical construction of infons in terms of representations and informational equivalences between them. The main theme of the paper arose from an electronic mail exchange with Pat Hayes of Xeroxparc. The exposition derives from a talk I gave at theTheories of (...) Partial Information conference held at the University of Texas at Austin, January 1990. (shrink)

Various equivalents and weakenings of the combinatorial principle $\diamond$ 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 $\omega_1$.

We consider various strengthenings of the combinatorial principle ⋄ + which are provable from V = L, and give applications in set theory.