¬(∀ b0. b0 = a ∨ b0 ∈ s → b0 < b), ∀ b0. b0 ∈ s → b0 < b ⊦ ¬ a < b
¬ a < b, ∀ b0. b0 ∈ s → b0 < b ⊦ ¬(∀ b0. b0 = a ∨ b0 ∈ s → b0 < b)