Generating countable sets of surjective functions
James D. Mitchell, Y. Péresse · Fundamenta Mathematicae · 2011
We prove that any countable set of surjective functions on an infinite set of cardinality $\aleph_n$ with $n\in\mathbb N$ can be generated by at most $n^2/2+9n/2+7$ surjective functions of the same set; and there exist $n^2/2+9n/2+7$ surjective functions