∀x:ℕ. (∃r:ℕ [(((r * r) ≤ x) ∧ x < (r + 1) * (r + 1))])
{ TACTIC:((D 0 THENA Auto) THEN CaseNat 0 `x') }
1. x : ℕ@i
2. x = 0 ∈ ℤ
⊢ ∃r:ℕ [(((r * r) ≤ 0) ∧ 0 < (r + 1) * (r + 1))]
1. x : ℕ@i
2. ¬(x = 0 ∈ ℤ)
⊢ ∃r:ℕ [(((r * r) ≤ x) ∧ x < (r + 1) * (r + 1))]