exact h x (lt_of_lt_of_le (lt_of_mem hx) (by simp)) |>.mp hx
case h.mp
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
u a b : M
h : ∀ x < u + (a + b + 1) ^ 2, x ∈ u ↔ ∃ y ∈ a, ∃ z ∈ b, x = ⟪y, z⟫
x : M
hx : x ∈ u
⊢ ∃ y ∈ a, ∃ z ∈ b, x = ⟪y, z⟫
no goals