∀ {α : Type u} {β : α → Type v} [inst : SizeOf α] [inst_1 : (a : α) → SizeOf (β a)] (size : ℕ) (k : α) (v : β k)
  (l r : Std.DTreeMap.Internal.Impl α β),
  sizeOf (Std.DTreeMap.Internal.Impl.inner size k v l r) = 1 + sizeOf size + sizeOf k + sizeOf v + sizeOf l + sizeOf r