Goal:
  
  A : Type
  P : list A → list A → A → A → Type
  Γ : list A
  Γ' : list A
  Γl : list A
  Γr : list A
  ============================
   (All2_fold P Γ Γl
    → All2_fold (All_over P Γ Γl) Γ' Γr → All2_fold P (Γ' ++ Γ) (Γr ++ Γl))


DEBUG:Going to execute:
induction 2; auto; simpl; constructor