Fuzzy inequational logic

• A truth-functional logic for reasoning with graded inequalities is proposed.
• Its semantics is defined using algebras with fuzzy orders.
• Completeness in the Pavelka style is established for all complete residuated lattices.
• A complete abstract logic of graded attributes is shown as an application.

We present a logic for reasoning about graded inequalities which generalizes the ordinary inequational logic used in universal algebra. The logic deals with atomic predicate formulas of the form of inequalities between terms and formalizes their semantic entailment and provability in graded setting which allows to draw partially true conclusions from partially true assumptions. We follow the Pavelka approach and define general degrees of semantic entailment and provability using complete residuated lattices as structures of truth degrees. We prove the logic is Pavelka-style complete. Furthermore, we present a logic for reasoning about graded if–then rules which is obtained as particular case of the general result.