exact irrefl_of _ _ $ lt_of_lt_of_le h this
L : Language
ξ : Type u_1
n n₁ n₂✝ n₂ m m₁ m₂ m₃ : ℕ
p : SyntacticSemiformula L n
h : (fvarList p).toFinset.sup id < m
hm : m ∈ fvarList p
this : m ≤ (fvarList p).toFinset.sup id
⊢ False
no goals