V A Bazhanov, The imaginary geometry of N I Lobachevskii and the imaginary logic of N A Vasiliev, Modern Logic 4 (2) (1994), 148-156. http://www-history.mcs.st-andrews.ac.uk/References/Lobachevsky.html

"Platon Poretsky worked as an astronomer and observer first at Kharkov Observatory and then at Kazan University. He became interested in logic through Vasiliev just before he retired in 1889 through ill health." http://www-history.mcs.st-andrews.ac.uk/Mathematicians/Poretsky.html