On Nonregular Ultrafilters. - Jussi Ketonen (J. Symb. Log., 1972)

EKL - A Mathematically Oriented Proof Checker. - Jussi Ketonen (CADE, 1984)

A Decidable Fragment of Predicate Calculus. - Jussi Ketonen; Richard W. Weyhrauch (Theor. Comput. Sci., 1984)

A Decision Procedure Revisited: Notes on Direct Logic, Linear Logic and its Implementation. - Gianluigi Bellin; Jussi Ketonen (Theor. Comput. Sci., 1992)