  Relativistic three-dimensional quasipotential (equal-time) equations are
considered, which describe bound states of fermion and boson of spin S=0 or
S=1. The spin structure of the interaction quasipotentials in such systems is
studied, and corresponding partial-wave equation for the simplest case is
obtained. Such equations can be used in calculations of energy spectra, decay
rates and structure functions of quark-diquark systems (nucleons and their
resonances) as well as for description of ($\pi\mu$)- atom.
