 Other results in his research include a proof that a metrizable topological space has a non-Archimedean metric (satisfying the "strong triangle inequality" "d"("x","z") ≤ max("d"("x","y"),"d"("y","z")) if and only if it has dimension zero, description of completely metrizable spaces in terms of cocompactness, and a topological characterization of Hilbert space.From 1962 onwards, his research primarily concerned the development of new topological theories