mathworld.wolfram.com
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MathWorld is a comprehensive online mathematics encyclopedia by Wolfram Research that provides concise, well-organized articles on many math topics. In propositional logic, you’ll find definitions, truth tables, logical operators, and related concepts with explanations, formulas, and cross-references to connected topics.
More resources on Propositional Logic
Introduction to Logic
This course is an introduction to Logic from a computational perspective. It shows how to encode information in the form of logical sentences; it shows how to reason with information in this form; and it provides an overview of logic technology and its applications - in mathematics, science, engineering, business, law, and so forth.
ProofWeb
Online logic tutor for propositional logic
forall x Logic Book
Free online textbook with propositional logic
Stanford Intro to Logic
Interactive exercises for propositional logic
Logic and Proofs
Learn propositional logic & mathematical proofs with this free MIT course. Master the fundamentals for computer science!
plato.stanford.edu
Stanford Encyclopedia of Philosophy (plato.stanford.edu) is a free, peer‑reviewed online encyclopedia of philosophy. It contains in‑depth, scholarly articles on a wide range of philosophical topics, including detailed entries on logic and propositional logic.