induction xs
xs : List VarName
P : Formula
Δ : Set Formula
h1 : IsDeduct Δ (Forall_ xs P)
⊢ IsDeduct Δ P
case nil
P : Formula
Δ : Set Formula
h1 : IsDeduct Δ (Forall_ [] P)
⊢ IsDeduct Δ P

case cons
P : Formula
Δ : Set Formula
head✝ : VarName
tail✝ : List VarName
tail_ih✝ : IsDeduct Δ (Forall_ tail✝ P) → IsDeduct Δ P
h1 : IsDeduct Δ (Forall_ (head✝ :: tail✝) P)
⊢ IsDeduct Δ P