apply IsDeduct.mp_ P
P Q : Formula
Δ : Set Formula
h1 : IsDeduct Δ (P.imp_ Q)
⊢ IsDeduct (Δ ∪ {P}) Q
case a
P Q : Formula
Δ : Set Formula
h1 : IsDeduct Δ (P.imp_ Q)
⊢ IsDeduct (Δ ∪ {P}) (P.imp_ Q)

case a
P Q : Formula
Δ : Set Formula
h1 : IsDeduct Δ (P.imp_ Q)
⊢ IsDeduct (Δ ∪ {P}) P