54Axx Generalities
 54A05 Topological spaces and generalizations (closure spaces, etc.)
 54A10 Several topologies on one set (change of topology, comparison of topologies, lattices of topologies)
 54A15 Syntopogeneous structures

54A20 Convergence in general topology (sequences, filters, limits, convergence spaces, etc.)
(1)
 54A25 Cardinality properties (cardinal functions and inequalities, discrete subsets) [See also 03Exx] (For ultrafilters, see 54D80)
 54A35 Consistency and independence results [See also 03E35]
 54A40 Fuzzy topology [See also 03E72]
 54A99 None of the above, but in this section