I've heard that decoherence does not completely solve "measurement problem" i.e. does not explain the final selection of one of the possible alternatives. In this sense may the Shrodinger cat problem be still considered unresolved?
One may start with a postulate that for a particular observable the states for which it has uniquly defined measured value ##a_i## are orthogonal: ##\langle\psi_i|\psi_j\rangle=0## for ##i\neq j##
Without loosing of generality, we can also normalize them and further consider them orthonormal...
All right, I now see that my answer was not quite correct. Now I much hope to have the right answer.
Contrary to what I said previously, there is no interference pattern on D0 even for events for which any of two detectors D1 or D2 detected a particle. But there is an interference pattern on D0...