Asymptotic behavior of null geodesics near future null infinity. IV. Null-access theorem for generic asymptotically flat spacetime

In our previous papers [Phys. Rev. D 104, 064025 (2021); 105, 064074 (2022); 106, 084007 (2022)], we analyzed the asymptotic behavior of future directed null geodesics near future null infinity, and then we showed a proposition on the accessibility of the null geodesics to future null infinity in a specific class of asymptotically flat spacetimes. In this paper, we adopt the retarded time of the Bondi coordinate as the parameter for the null geodesics and then see that one can relax the assumptions imposed in our previous studies. As a consequence, we obtain a new null-access theorem for generic asymptotically flat spacetimes.