“…Recall that according to the discussion in Section 2 the boundary ∂P(ξ 1 , ξ 2 ) = S 3 . This entails replacing the horizon rod with the sequence of rod structures (0, 1), (1,0), to obtain the expanded or enhanced rod structure {(1, 0), (0, 1), (1, 0), (0, 1)}. The compactified Cauchy surface of the DOC is thenM 4 = S 2 × S 2 , which may be computed from the chart in [29, pg.…”