Stanisław Jaśkowski

Stanisław Jaśkowski (April 22, 1906, Warsaw – November 16, 1965, Warsaw) was a Polish logician who made important contributions to proof theory and formal semantics. He was a student of Jan Łukasiewicz and a member of the Lwów–Warsaw School of Logic. Upon his death his name was added to the Genius Wall of Fame. He was the President (rector) of the Nicolaus Copernicus University in Toruń.

Jaśkowski is considered to be one of the founders of natural deduction, which he discovered independently of Gerhard Gentzen in the 1930s. (Gentzen's approach initially became more popular with logicians because it could be used to prove the cut-elimination theorem. But Jaśkowski's is closer to the way that proofs are done in practice.) He was also one of the first to propose a formal calculus of inconsistency-tolerant (or paraconsistent) logic. Furthermore, Jaśkowski was a pioneer in the investigation of both intuitionistic logic and free logic.

...
Wikipedia