Stuck on formal proof, missing one step I'm stuck on what to put for step 7. Thank you! 1. Horned(c) → (Elusive(c) ∧ Dangerous(c)) 2. (Elusive(c) ∨ Mythical(c)) → Rare(c) 3. Mammal(c) → ¬Rare(c) 4. Horned(c) 5. Mammal(c) 6. ¬Rare(c) (→ Elim 5, 3) 7. ? 8. ⊥ (Rule ?) 9.¬Mammal(c) (¬Intro 5-8) **Goal 10.** Horned(c) → ¬Mammal(c)

You need more than just 1 more step, but you are almost there:

7. $Elusive(c) \land Dangerous(c) \: (\rightarrow Elim 1,4)$

8. $Elusive(c) \: (\land Elim \: 7)$

9. $Elusive(c) \lor Mythical(c) \: (\lor Intro \: 8)$

10. $Rare(c) \: (\rightarrow Elim \: 2,9)$

11. $\bot \: (\bot Intro \: 6, 10)$