simp at *
X : Finset Formula
ψ ϕ : Formula
psi_in_X : ψ ∈ X
sub_voc : voc ϕ ⊆ voc ψ
⊢ voc (X \ {ψ} ∪ {ϕ}) ⊆ voc X
X : Finset Formula
ψ ϕ : Formula
psi_in_X : ψ ∈ X
sub_voc : vocabOfFormula ϕ ⊆ vocabOfFormula ψ
⊢ vocabOfFormula ϕ ∪ (X.erase ψ).biUnion vocabOfFormula ⊆ X.biUnion vocabOfFormula