several crossings of levels with different angular momentum will normally occur.

Most applications in the literature deal with exotic atoms, but the phenomenon was first revealed in the context of condense-matter physics, and could well find new applications there. Layers could be combined, with a variety of voltages, and a variety of interlayer distances, and the situation can perhaps be realised where a tiny change of one of the voltage could provoke a sudden change of the bound state spectrum.

The problem of particles in a trap, with individual confinement and an additional pairwise interaction, has stimulated a copious literature, but the level rearrangement occurring at the transition from individual binding to pairwise binding was never underlined, at least to our knowledge.

Several further investigations could be done. The problem of absorption has already been mentioned, and it is our intent to study it in some detail. The subject is already documented in the case of exotic atoms, as pions, kaons and especially antiprotons have inelastic interaction with the nucleus. It has been shown that the phenomenon of rearrangement disappears if the absorptive component of the interaction becomes too strong. See, e.g., [@Badalyan:1982; @Gal:1996pr] and refs. there.

It could be 