A metric space X is ultra-m-separable if the weight of the Katetov hull, E(X), of X is no greater than m. It is shown that the collection of all nonempty ultra-m-separable subsets of X is an ideal closed under taking the limit of its members with respect to the Hausdorff distance. As an application of this, it is proved that if (K, d_k) is precompact and (X.d_x) is ultra-m-separable. then (K × X, D) is ultra-m-separable as well, where D is any metric onK×X such that D((u,x). (u, y)) = d_x(x, y) and D((u,x), (v,x)) = d_k(u, v) for any u, v ∈ K and x, y ∈ X. Bounded ultra-m-separable spaces are characterized by means of their metrically discrete subsets.
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