simp only [finset_var_name_max_len]
x hd : VarName
tl : Finset VarName
a1 : hd ∉ tl
ih : x ∈ tl → x.length ≤ Finset.fold (fun m n => max m n) 0 (String.length ∘ VarName.toString) tl
c1 : x ∈ tl
⊢ x.length ≤ finset_var_name_max_len (insert hd tl)
x hd : VarName
tl : Finset VarName
a1 : hd ∉ tl
ih : x ∈ tl → x.length ≤ Finset.fold (fun m n => max m n) 0 (String.length ∘ VarName.toString) tl
c1 : x ∈ tl
⊢ x.length ≤ Finset.fold (fun m n => max m n) 0 (String.length ∘ VarName.toString) (insert hd tl)