The Bergman-Shelah Preorder on Transformation Semigroups

Z. Mesyan, J. D. Mitchell, M. Morayne +1

Let $\nat^\nat$ be the semigroup of all mappings on the natural numbers $\nat$, and let $U$ and $V$ be subsets of $\nat^\nat$. We write $U\preccurlyeq V$ if there exists a countabl…