The Souslin number in set-theoretic topology

Abstract

This paper presents a short survey of some directions in the theory of cardinal functions, in which estimations containing the Souslin number play the central role. Together with the known facts, the paper contains some new results established by the author. In Section 4 three very general formulae are proved; we use these formulae in the proof of the main result of the paper (Theorem 5.17) about the strict ap-caliber.