On classes of Banach spaces admitting ‘‘small” universal spaces
On classes of Banach spaces admitting ‘‘small” universal spaces
We characterize those classes $\mathcal {C}$ of separable Banach spaces admitting a separable universal space $Y$ (that is, a space $Y$ containing, up to isomorphism, all members of $\mathcal {C}$) which is not universal for all separable Banach spaces. The characterization is a byproduct of the fact, proved in the …