FROM SEP:

Logical Constants: http://plato.stanford.edu/entries/logical-constants/

Logic and Ontology: http://plato.stanford.edu/entries/logic-ontology/

Early Foundation I (Principia): http://plato.stanford.edu/entries/principia-mathematica/

Early Foundation II (Frege): http://plato.stanford.edu/entries/frege/

Early Foundation III (Goedel): http://plato.stanford.edu/entries/goedel/

Early Foundation IV (Tarski): http://plato.stanford.edu/entries/tarski-truth/

Logic and Games: http://plato.stanford.edu/entries/logic-games/

Truth and Consequence I: http://plato.stanford.edu/entries/logical-consequence/

Truth and Consequence II: http://plato.stanford.edu/entries/logical-truth/

Truth and Consequence III (paradoxes): http://plato.stanford.edu/entries/paradoxes-contemporary-logic/

Truth and Consequence IV (Russell's paradox): http://plato.stanford.edu/entries/russell-paradox/

Automated Theorem Proving: http://plato.stanford.edu/entries/reasoning-automated/

Axiomatizing truth: http://plato.stanford.edu/entries/truth-axiomatic/

Computability: http://plato.stanford.edu/entries/computability/

Contradiction: http://plato.stanford.edu/entries/contradiction/