Theorem: LO.FirstOrder.Arith.Model.insert_eq_union_singleton (Arithmetization/ISigmaOne/HFS/Basic.lean)

State before:
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
a s x : M
⊢ x ∈ insert a s ↔ x ∈ {a} ∪ s
Tactic:
simp
State after:
no goals