Special Logic Formula Tautology Contradiction Satisfiable (重言式，永真式) (矛盾式，永假式) Formula (可能式，可满足式) ·Always TRUE for all ·Always FALSE for all ·Can be TRUE for some possible assignments possible assignments possible assignments (p→q)→(q→p) pΛp (p→q)pVq)Special Logic Formula • Always TRUE for all possible assignments (𝒑 → 𝒒) ⟷ (¬𝒒 → ¬𝒑) Tautology (重言式，永真式) • Always FALSE for all possible assignments 𝒑 ∧ ¬𝒑 Contradiction (矛盾式，永假式) • Can be TRUE for some possible assignments (𝒑 → 𝒒) ∧ (𝒑 ∨ 𝒒) Satisfiable Formula (可能式，可满足式)