focal point

nLab focal point Contents Context Topology topology (point-set topology, point-free topology) see also differential topology, algebraic topology, functional analysis and topological homotopy theory Introduction Basic concepts - open subset, closed subset, neighbourhood - topological space, locale - base for the topology, neighbourhood base - finer/coarser topology - closure, interior, boundary - separation, sobriety - continuous function, homeomorphism - uniformly continuous...