let S := { i | z ≤ s (i + 1) }
s : ℕ → ℤ
hs : ∀ (i : ℕ), s i < s (i + 1)
z : ℤ
hs0 : s 0 < z
hmono : StrictMono s
⊢ ∃! i, s i < z ∧ z ≤ s (i + 1)
s : ℕ → ℤ
hs : ∀ (i : ℕ), s i < s (i + 1)
z : ℤ
hs0 : s 0 < z
hmono : StrictMono s
S : Set ℕ := {i | z ≤ s (i + 1)}
⊢ ∃! i, s i < z ∧ z ≤ s (i + 1)