Essays on mathematical and philosophical logic : proceedings of the Fourth Scandinavian Logic Symposium and of the First Soviet-Finnish Logic Conference, Jyväskylä, Finland, June 29-July 6, 1976 / edited by Jaakko Hintikka, Ilkka Niiniluoto, and Esa Saarinen / Jaakko Hintikka, Ilkka Niiniluoto, ほか