simp only [if_pos c1_left] at phi_ih
Δ_U : Set Formula
V : VarBoolAssignment
phi psi : Formula
phi_ih :
  ↑phi.primeSet ⊆ Δ_U →
    IsDeduct ((fun a => if evalPrime V a then a else a.not_) '' Δ_U) (if evalPrime V phi then phi else phi.not_)
psi_ih :
  ↑psi.primeSet ⊆ Δ_U →
    IsDeduct ((fun a => if evalPrime V a then a else a.not_) '' Δ_U) (if evalPrime V psi then psi else psi.not_)
h1_left : ↑phi.primeSet ⊆ Δ_U
h1_right : ↑psi.primeSet ⊆ Δ_U
c1_left : evalPrime V phi
c1_right : ¬evalPrime V psi
⊢ IsDeduct ((fun a => if evalPrime V a then a else a.not_) '' Δ_U) (phi.imp_ psi).not_
Δ_U : Set Formula
V : VarBoolAssignment
phi psi : Formula
psi_ih :
  ↑psi.primeSet ⊆ Δ_U →
    IsDeduct ((fun a => if evalPrime V a then a else a.not_) '' Δ_U) (if evalPrime V psi then psi else psi.not_)
h1_left : ↑phi.primeSet ⊆ Δ_U
h1_right : ↑psi.primeSet ⊆ Δ_U
c1_left : evalPrime V phi
c1_right : ¬evalPrime V psi
phi_ih : ↑phi.primeSet ⊆ Δ_U → IsDeduct ((fun a => if evalPrime V a then a else a.not_) '' Δ_U) phi
⊢ IsDeduct ((fun a => if evalPrime V a then a else a.not_) '' Δ_U) (phi.imp_ psi).not_