On the Riemann–Hilbert problem and the oblique derivative problem at the plane with sections along the circumference

The researches done before (Math. Modell. 2(4), 143–154) which concern the solving of the oblique derivative problem for harmonic functions at the set of sections are continued. The question about equivalence of the oblique derivative problem at the plane with sections along the circumference for harmonic functions and corresponding Riemann–Hilbert problem is studied. The general enough case for which both problems can be solved in an explicit form is considered.