Combinatorial principles concerning approximations of functions. Petr Hájek, Jeff Paris (1987) Archiv für mathematische Logik und Grundlagenforschung
Completion closed algebras and models of Peano arithmetic Petr Hájek (1981) Commentationes Mathematicae Universitatis Carolinae
Consistency proof without transfinite induction for a formal system for turing machines. Salvatore Caporaso (1978) Archiv für mathematische Logik und Grundlagenforschung
Constructing Kripke models of certain fragments of Heyting's arithmetic. Wehmeier, Kai F. (1998) Publications de l'Institut Mathématique. Nouvelle Série