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syllogistic logic
Calculus Ratiocinator
predicate logic
dhātī (essential/intrinsic) modalities
summa logicae
propositional logic foundations
Boolean algebra
Isagoge
calculus of relations
logical syntax of language
Principia Mathematica
incompleteness theorems
two Dogmas of Empiricism
¬(P ∧ Q) <=> (¬P) ∨ (¬Q)
possible worlds semantics
indefinability of truth theorem