Three-dimensional covariant one-time equations for a system of $n$ spinor particles

Covariant three-dimensional equations for the wave function of a bound state are obtained on the basis of the field-theoretical Green's functions that give a one-time description of a system of $n$ fermions. The explicit form of the interaction operators that occur in these equations is determined, together with the normalization conditions of the wave function. A baryon as a bound state of three quarks is considered as an example.