Redheffer products and characteristic functions (Q1910097)

The author extends some computations [due to \textit{P. A. Fuhrman}: Isr. J. Math. 16 (1973), 162-175 (1974; Zbl 0301.47020), and \textit{J. A. Ball} and \textit{A. Lubin}: Pac. J. Math. 63, 309-323 (1976; Zbl 0325.47010)] of the characteristic functions of completely non-unitary contractions, via Redheffer products. Strong interactions with linear systems theory, which is the original framework of Redheffer products, and with a classical by now functional model due to De Branges and Rovnyak are amply discussed in the paper.