exact Eq.symm <| under_inj.mp this
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
x s : M
h : Seq s
this : under (lh s + 1) = under (lh (s ⁀' x))
⊢ lh (s ⁀' x) = lh s + 1
no goals