Definition
Unsatisfiability–Validity Duality (Propositional Logic)
A formula
is unsatisfiable if and only if its negation is valid: In other words,
is a contradiction exactly when is a tautology.
Reason
Mirror image of the validity–unsatisfiability duality
The claim is the validity–unsatisfiability duality applied to
in place of : since [[Knowledge/Double Negation Elimination| is equivalent to ]],