Penner uses the mathematical symbol ∃, the existential quantifier, to state the proof: "To see that 0 is even, we must prove that ∃k (0 = 2k), and this follows from the equality 0 = 2 ⋅ 0."
Ο Penner χρησιμοποιεί το μαθηματικό σύμβολο ∃, το υπάρχει, για να δηλώσει την απόδειξη: "To see that 0 is even, we must prove that ∃k (0 = 2k), and this follows from the equality 0 = 2 ⋅ 0."