“…The functor U : E → Set is said to be topological, and E is said to be a topological category over Set, if U is concrete (i.e., faithful and amnestic, (i.e., if U (f ) = id and f is an isomorphism, then f = id )), has small (i.e., set) fibers, and for which every U -source has an initial lift or, equivalently, for which each U -sink has a final lift [19,21,26] or [29].…”