Suppose an extension map U: T-1 -> T-0 in the 2-category Con of contexts for arithmetic universes satisfies a Chevalley criterion for being an (op)fibration in Con. If M is a model of T-0 in an elementary topos S with nno, then the classifier p: S[T-1/M] -> S satisfies the representable definition of being an (op)fibration in the 2-category epsilon Iop of elementary toposes (with nno) and geometric morphisms.