# Well formulated formula?

Logic Level 1

According to propositional logic, which of the following is not a well formulated formula?

(1): ($$A \wedge B) \to (C \vee D)$$
(2): ($$A \neg B) \to (C \vee D)$$
(3): ($$A \leftrightarrow B) \to (\neg D)$$

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