Key points are not available for this paper at this time.
A definition of an asymptotically flat ℋ-space is given. Using a technique for solving for all null geodesics in an ℋ-space, it is shown that the construction of another ℋ-space from a given asymptotically flat ℋ-space is idempotent, i.e., the new ℋ-space is isometric to the first one.
Ludvigsen et al. (Wed,) studied this question.