∀ {α : Type u} [inst : Std.PRange.UpwardEnumerable α] [inst_1 : Std.PRange.LawfulUpwardEnumerable α]
  [inst_2 : Std.PRange.InfinitelyUpwardEnumerable α] (n : ℕ) (a : α),
  Std.PRange.succMany n a = (Std.PRange.succMany? n a).get ⋯