1. J.A. Ball, I. Gohberg and M.A. Kaashoek, Nevanlinna-Pick interpolation for timevarying input-output maps: the discrete case, in:Time-variant systems and interpolation (Ed. I. Gohberg), OT 56, Birkhäuser Verlag, Basel, 1992, pp. 1?51.
2. J.A. Ball, I. Gohberg and M.A. Kaashoek, Nevanlinna-Pick interpolation for timevarying input-output maps: the continuous case, in:Time-variant systems and interpolation (Ed. I. Gohberg), OT 56, Birkhäuser Verlag, Basel, 1992, pp. 52?89.
3. J.A. Ball, I. Gohberg and M.A. Kaashoek, Bitangential interpolation for input-output operators of time-varying systems: the discrete case,Operator Theory: Advances and Applications 64 (1993), 33?72.
4. J.A. Ball, I. Gohberg and M.A. Kaashoek, Input-output operators ofJ-unitary time-varying continuous time systems, to appear in Zaanen-volume.
5. J.A. Ball, I. Gohberg and M.A. Kaashoek, Two sided Nudelman interpolation for input-output operators of discrete time-varying systems, to appear.