  The main content of this paper is Lectures 5 and 6 that continue lecture
notes [20]. Content of Lectures 1-4 of [20] is reviewed for the reader's
convenience in sections 1-4, respectively. It is shown in Lecture 5 how
residual parts of the minimal unitary extensions, that correspond to solutions
of the problem, yield some boundary properties of the coefficient
matrix-function. These results generalize the classical Nevanlinna - Adamjan -
Arov~- Krein theorem. Lecture 6 discusses how further properties of the
coefficient matrices follow from denseness of certain sets in the associated
function model spaces. The structure of the dense set reflects the structure of
the problem data.
