The correspondence of the previously given relativistic quantum mechanics of spinless or spin 1/2 particle with the quantum nonrelativistic and the classical relativistic mechanics is proved. In the Galilean quantum case the appearance of the familiar transformation phase factor is explained and the origin of the mass superselection rule indicated. In the relativistic classical case the equation for trajectories and the covariant equation of motion for spin are obtained. The conditions are found under which the usual theory of relativistic wave equations is of relevance (in some particular reference frame).
It is shown that ideality of meson octet-singlet and 15-plet-singlet mixing can be obtained from requirement of vanishing of definite set of exotic commutators. Enlargement of the set does not lead to mass degeneration (as it happens for the octet and 15-plet) but it leaves the ideal mass formulae unchanged.
After Dirac had firmly planted the concept of a magnetic monopole in the minds of experimental and theoretical physicists the search for this particle has not stopped. Since it can manifest itself only through the interaction with ordinary matter many matter-monopole systems have been investigated. The purpose of the present paper is to give a short and therefore incomplete review of the literature concerning the question whether an electron, a proton or an atom can be bound to a magnetic monopole.
