Relativistic addition of direct interactions in the point form of dynamics

Dirac's problem of a Hamiltonian relativistic description of directly interacting particles is formulated as the problem of adding (combining) primary interactions given in the form of Lorentz-invariant Hermitian operators. For the case of three particles (with spins 0 and 1/2 ) the general solution to the problem in the framework of the point form of dynamics is found.