In the ’60s, B. Sz.-Nagy and C. Foiaş developed a functional model for a completely nonunitary contraction on a complex separable Hilbert space [Harmonic analysis of operators on Hilbert space (1967; Zbl 0157.432)]. It says that such an operator is unitarily equivalent to a restriction of the orthogonal sum of a backward shift and a bilateral shift. In this note, the author constructs explicitly the shift operators in question, the space of the restriction as well as the implementing unitary operators in terms of T. The method is elementary and self-contained. It generalizes Rota’s contruction for the case when \(T^ n\) converges strongly to 0 as n approaches \(\infty\).