Jan Lukasiewicz

First of all, it's spelled Jan Lukasiewicz, with a `k'; also, there is a bar through the L. It's pronounced `Woo kah SHAY vich'.

Second, it is a common misconception that Lukasiewicz invented reverse polish notation. In fact, he did not; he invented what is known as Polish notation, a bracketless representation of propositional and predicate logic. In logic, Polish notation uses the following symbols:

• Np (negation) = ¬p
• Kpq (conjunction) = p ^ q
• Apq (disjunction) = p v q
• Cpq (implication (material implication, to be precise)) = p -> q
• Epq (equivalence (material equivalence)) = p <-> q
• PxFx (universal quantification) = \forall x F(x)
• SxFx (existential quantification) = \exists x F(x)

RPN is called `reverse' because it was based on the preexisting Polish notation. Postfix (and prefix) notations for logic and arithmetic surely existed before Lukasiewicz; it was his notation, though, that gained the widest popularity.

In addition to RPN, Cambridge Polish notation (a parenthesised prefix notation, used in Lisp) is named after Lukasiewicz's Polish notation.

Lukasiewicz was also well-known for his work on three-valued logics---probably much more important in the long run than his particular usage of prefix notation.

Lukasiewicz also studied Aristotelian, Stoic and other nonmodern logics. One of his early works is On Aristotle's Principle of Contradiction. Due to such studies, Lukasiewicz had a better sense of the history of logic than, say, Bertrand Russell did.

In addition to his three-valued logic, Lukasiewicz developed an infinite-valued logic, with truth values on the reals from 0 (false) to 1 (true). No, this did not originate with Lotfi Zadeh. Zadeh's first paper on fuzzy set theory has a footnote indicating that his theory comes from a modification of Lukasiewicz's.