Goal:
    A : Type  P : list A → A → Type  Γ : list A  Δ : list A
  ============================
   (All_fold P (Γ ++ Δ)
    → All_fold P Δ × All_fold (λ Γ : list A, P (Γ ++ Δ)) Γ)


DEBUG:Going to execute:
induction Γ in Δ |- *; split