scientific article published in June 1960

scientific article published in 1993

scientific article published in 1973

scientific article published in January 1985

scientific article published in 1978

scientific article published in 1972

doctoral dissertation by Kazimierz Urbanik

scientific article published in 1964

Published in "Bulletin de l’Académie Polonaise des Sciences, Série des Sciences Mathématiques, Astronomiques et Physiques"

scientific article published in March 1956

scientific article published in 1957