ABASHNIK, V. O. CHRISTOPH SIGWART (1830–1904) AND HIS LOGIC IN THE WORKS OF ISIDOR PRODAN (1854–1919/1920). The Journal of V. N. Karazin Kharkiv National University, Series Philosophy. Philosophical Peripeteias, n. 63, p. 80-88, 30 Dec. 2020.