  On the basis of our recent model of a one-dimensional (1D) completed
scattering we argue that Leggett's principles of macroscopic realism must and
can be extended onto the level of single electrons and atoms. These principles
need three quite feasible innovations in quantum mechanics (QM): (1) at the
conceptual level, QM must treat a pure time-dependent one-particle state to
involve two or more macroscopically distinct alternatives for a particle as a
pure {\it combined} one - the intermediate link between a pure {\it elementary}
state (indecomposable into macroscopically distinct parts) and statistical
mixture; (2) at the mathematical level, QM must provide the presentation of the
pure time-dependent combined state as a coherent superposition of
macroscopically distinct elementary states (MDESs); (3) at the experimental
level, QM must provide for such states two types of measurements - those for
observing the interference pattern resulting from the joint action of MDESs,
and non-demolishing 'which-way' measurements for scanning the individual
properties of MDESs.
