Solution
= Solution
With both final splitters removed, the path labels map directly into detector labels:
$$
\boxed{|\Psi_{RR}\rangle=-\frac12|\gamma\rangle+\frac12\left(i|cd\rangle+i|dc\rangle+|dd\rangle\right).}
$$
In particular $P_{RR}(C^+,C^-)=0$, because joint occupation of the two intersecting arms has already annihilated. Each of the other three charged-particle coincidences has unconditional <probability> $1/4$.