  We prove that the Nevalinna-Pick algorithm provides different homeomorphisms
between certain topological spaces of measures, analytic functions and
sequences of complex numbers. This algorithm also yields a continued fraction
expansion of every Schur function, whose approximants are identified. The
approximants are quotients of rational functions which can be understood as the
rational analogs of the Wall polynomials. The properties of these Wall rational
functions and the corresponding approximants are studied. The above results
permit us to obtain a Khrushchev's formula for orthogonal rational functions.
An introduction to the convergence of the Wall approximants in the
indeterminate case is also presented.

Classical Analysis and ODEs