Use Fitch to formalize the proofs you gave of their validity.
( ¬Mythical(c) (arrow pointing to mammal) Mammal(c)) (upside down V) (Mythical(c) (arrow pointing to mortal) ¬Mortal(c))
(¬Mortal(c) V Mammal(c)) (arrow pointing to horned) Horned(c)
Horned(c) (arrow pointing to magical) Magical(c)
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Magical(c)