Note 65 — Chapter XXVIII · THE CONSTRUCTION OF POINTS[59]
Reading edition
He defines a topological space as "normal" when any two non-overlapping closed manifolds and can be separated by two non-overlapping regions , which respectively contain them and have no boundary-points. Ib., p. 310, and Hausdorff, op. cit., p. 215. A "boundary-point" of a collection is one which has a neighbourhood that is not a sub-class of the collection.