A new proof of the support theorem and the range characterization for the Radon transform. Bernd Droste (1983) Manuscripta mathematica
A quadratic integral equation Roger D. Nussbaum (1980) Annali della Scuola Normale Superiore di Pisa - Classe di Scienze
Algebraic representation of the Nakajima-Zvanzig's generalized master equation Lubomír Skála, Oldřich Bílek (1982) Acta Universitatis Carolinae. Mathematica et Physica