  Delayed-choice erasure is investigated in two-photon two-slit experiments
that are generalizations of the micromaser experiment of Scully et al. [Scully,
M. O. et al. Nature 351, 111-116 (1991)]. Applying quantum mechanics to the
localization detector, it is shown that erasure with delayed choice in the
sense of Scully, has an analogous structure as simple erasure. The description
goes beyond probabilities. The EPR-type disentanglement, consisting in two
mutually incompatible distant measurements, is used as a general framework in
both parts of this study. Two simple coherence cases are shown to emerge
naturally, and they are precisely the two experiments of Scully et al. The
treatment seems to require the relative-reality-of-unitarily-evolving-state
(RRUES) approach. Besides insight in the exoeriments, this study has also the
goal of insight in quantum mechanics. The question is if it can be more than
just a "book-keeping device" for calculating probabilities as Scully et al.
modestly and cautiously claim.
