subst c_in
α : Formula
L R : Finset Formula
α_in_L : α ∈ L
c : TNode
φ φ' : Formula
precond_eq : ~~φ = α
L_cond_in : ~~φ' ∈ L
c_in : c = (insert φ' (L.erase (~~φ')), R)
⊢ (α = φ' ∨ ¬α = ~~φ') ∨ φ = φ' ∨ ¬φ = ~~φ' ∧ φ ∈ L
α : Formula
L R : Finset Formula
α_in_L : α ∈ L
φ φ' : Formula
precond_eq : ~~φ = α
L_cond_in : ~~φ' ∈ L
⊢ (α = φ' ∨ ¬α = ~~φ') ∨ φ = φ' ∨ ¬φ = ~~φ' ∧ φ ∈ L