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