case zero =>
  intro ha
  have : 0 < a := pos_of_lt_length ha
  exact ⟨1, pos_iff_one_le.mp this, by simp⟩
M : Type u_1
inst✝⁵ : Zero M
inst✝⁴ : One M
inst✝³ : Add M
inst✝² : Mul M
inst✝¹ : LT M
inst✝ : M ⊧ₘ* 𝐈𝚫₀
a : M
⊢ 0 < ‖a‖ → ∃ y ≤ a, Exponential 0 y
no goals