Stanisław Leśniewski, or Stanisław Leshniewski, (born March 30, 1886, Serpukhov, Russia—died May 13, 1939, Warsaw), Polish logician and mathematician. As a professor at the University of Warsaw (1919–39), he became a cofounder and leading representative of the Warsaw school of logic. His distinctive contribution was the construction of three interrelated formal systems, to which he gave the Greek-derived names of protothetic, ontology, and mereology.
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