Cardinal Well-foundedness and Choice

Abstract

We consider several notions of well-foundedness of cardinals in the absence of the Axiom of Choice. Some of these have been conflated by some authors, but we separate them carefully. We then consider implications among these, and also between these and other consequences of Choice. For instance, we show that the Partition Principle implies that all of our versions of well-foundedness are equivalent. We also show that one version, concerning surjections, implies the Dual Cantor-Schr\"oder-Bernstein theorem. It has been conjectured that well-foundedness, in one form or another, actually implies the Axiom of Choice, but this conjecture remains unresolved.