next x_lt_n =>
exfalso
have h_range_size : (Array.range n).size = n := Array.range_size
simp only [Array.range, Array.mkEmpty_eq] at h_range_size
simp only [x_eq_n, Array.mkEmpty_eq, h_range_size, Nat.lt_irrefl] at x_lt_n
case inr.isTrue
x n : Nat
ih : ∀ (h : x < n), (Array.range n)[x] = x
h : x < n + 1
x_eq_n : x = n
h✝ : x < (Nat.fold (flip Array.push) n (Array.mkEmpty (n + 1))).size
⊢ (Nat.fold (flip Array.push) n (Array.mkEmpty (n + 1)))[x] = x
no goals