simp
X : Finset Formula
ϕ : Formula
notin : ϕ ∉ X
⊢ setFormulaHasLength.1 (insert ϕ X) = setFormulaHasLength.1 X + lengthOfFormula ϕ
X : Finset Formula
ϕ : Formula
notin : ϕ ∉ X
⊢ (insert ϕ X).sum lengthOfFormula = X.sum lengthOfFormula + lengthOfFormula ϕ