Rekursive Funktionen in mehrsortigen Peano-Algebren. - Ulrich L. Hupbach (J. Inf. Process. Cybern., 1978)

Abstract Implementation of Abstract Data Types. - Ulrich L. Hupbach (MFCS, 1980)

On Behavioural Equivalence of Data Types. - Ulrich L. Hupbach; Horst Reichel (J. Inf. Process. Cybern., 1983)