Logical equivalence : Two compound propositions are logically equivalent means that they have the same truth values for all settings of truth values to their propositional variables.
Tautology: A compound proposition that evaluates to true for all settings of truth values to its propositional variables; it is abbreviated \(T\).
Contradiction: A compound proposition that evaluates to false for all settings of truth values to its propositional variables; it is abbreviated \(F\).
Contingency: A compound proposition that is neither a tautology nor a contradiction.