A Lower Bound for Generalized Dominating Numbers

Dan Hathaway

Published 2014-01-30, updated 2014-05-04Version 3

We show a new proof for the fact that when $\kappa$ and $\lambda$ are infinite cardinals satisfying $\lambda ^ \kappa = \lambda$, the cofinality of the set of all functions from $\lambda$ to $\kappa$ ordered by everywhere domination is $2^\lambda$. An earlier proof was a consequence of a result about independent families of functions. The new proof follows directly from the main theorem we present: for every $A \subseteq \lambda$ there is a function $f: {^\kappa \lambda} \to \kappa$ such that whenever $M$ is a transitive model of $\textrm{ZF}$ such that ${^\kappa \lambda} \subseteq M$ and some $g: {^\kappa \lambda} \to \kappa$ in $M$ dominates $f$, then $A \in M$. That is, "constructibility can be reduced to domination".