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Predicate functor logic
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<p>In <a href="/facts/Mathematical_logic/SaI7Y3wN">mathematical logic</a>, predicate functor logic (PFL) is one of several ways to express <a href="/facts/First-order_logic/lcISqWIg">first-order logic</a> (also known as <a href="/facts/Predicate_logic/lcISqWIg">predicate logic</a>) by purely algebraic means, i.e., without <a href="/facts/Quantification_(logic)/bgmvwxoo">quantified variables</a>. PFL employs a small number of algebraic devices called predicate functors (or predicate modifiers) that operate on terms to yield terms. PFL is mostly the invention of the <a href="/facts/Logic/8JnpJLtt">logician</a> and <a href="/facts/Philosopher/Hyvzc54m">philosopher</a> <a href="/facts/Willard_Quine/2RrhATxa">Willard Quine</a>. </p>