Description: Part of a study of the Axiom of Replacement used by the Isabelle prover.
In Isabelle, the sethood of PrimReplace is apparently postulated
implicitly by its type signature " [ i, [ i, i ] => o ]
=> i", which automatically asserts that it is a set without using any
axioms. To prove that it is a set in Metamath, we need the hypotheses
of Isabelle's "Axiom of Replacement" as well as the Axiom of Replacement
in the form funimaex . (Contributed by NM, 26-Oct-2006)