next n ih =>
simp only [Array.range, Nat.fold, flip, Array.size_push, Nat.succ.injEq]
simp only [Array.range, flip] at ih
exact ih
case succ
n✝ : Nat
a✝ : (Array.range n✝).size = n✝
⊢ (Array.range (n✝ + 1)).size = n✝ + 1
no goals