The strongly attached point topology of the abstract boundary for space-time

The abstract boundary construction of Scott and Szekeres provides a 'boundary' for any n-dimensional, paracompact, connected, Hausdorff, C ^∞ manifold. Singularities may then be defined as objects within this boundary. In a previous paper (Barry R A and Scott S M 2011 Class. Quantum Grav. 28 165003), a topology referred to as the attached point topology was defined for a manifold and its abstract boundary, thereby providing us with a description of how the abstract boundary is related to the underlying manifold. In this paper, a second topology, referred to as the strongly attached point topology, is presented for the abstract boundary construction. Whereas the abstract boundary was effectively disconnected from the manifold in the attached point topology, it is very much connected in the strongly attached point topology. A number of other interesting properties of the strongly attached point topology are considered, each of which support the idea that it is a very natural and appropriate topology for a manifold and its abstract boundary.