  The final state proposal [G.T. Horowitz and J.M. Maldacena, J. High Energy
Phys. 2004(2), 8 (2004)] is an attempt to relax the apparent tension between
string theory and semiclassical arguments regarding the unitarity of black hole
evaporation. The authors of [R. Bousso and D. Stanford, Phys. Rev. D 89, 044038
(2014)] analyze thought experiments where an infalling observer first verifies
the entanglement between early and late Hawking modes and then verifies the
interior purification of the same Hawking particle. They claim that
"probabilities for outcomes of these measurements are not defined" and
therefore suggest that "the final state proposal does not offer a consistent
alternative to the firewall hypothesis." We show, in contrast, that one may
define all the relevant probabilities based on the so-called ABL rule [Y.
Aharonov, P.G. Bergmann, and J.L. Lebowitz, Phys. Rev. 134, 1410 (1964)], which
is better suited for this task than the decoherence functional. We thus assert
that the analysis of Bousso and Stanford cannot yet rule out the final state
proposal.
