simp [show a - b = 0 from sub_spec_of_lt (not_le.mp hb)]
case neg
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
ha : ¬b + c ≤ a
hc : c ≤ a - b
hb : ¬b ≤ a
⊢ a - b - c = 0
no goals