simp [show a = 0 from by simpa using lt]
case inr.inr.inr
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* 𝐏𝐀⁻
a b c : M
lt✝¹ : a < 3
lt✝ : a < 2
lt : a < 1
⊢ a = 0 ∨ a = 1 ∨ a = 2 ∨ a = 3
no goals