SYMBOLS □ Necessarily ◇ Possibly ∴ Therefore ? Uncertain ¬ Not ∧ And ∨ Or → If...Then ↔ If and Only If ⊕ Either/Or (XOR) ∀ For All ∃ There Exists ∃! There Exists Exactly One ⊤ Always True ⊥ Always False | NAND ↓ NOR