by_cases Hs : Seq s <;> simp [Hs, ←Seq.domain_eq, lh_prop_of_not_seq]
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* 𝐈𝚺₁
s : M
⊢ (Seq s → ∃ d ≤ 2 * s, d = domain s ∧ d = under (lh s)) ∧ (¬Seq s → lh s = 0)
no goals