Goal:
  
  A : Type
  P : list A → list A → A → A → Type
  Pb : A → A → bool
  Γ : list A
  Δ : list A
  ============================
   (All2_fold (λ (_ _ : list A) (x x0 : A), Pb x x0) Γ Δ → forallb2 Pb Γ Δ)


DEBUG:Going to execute:
induction 1; simpl