Goal:
  
  X : Type
  x : X
  L : list (option X)
  t : list X
  l : list X
  H : Some (x :: l) = Some t
  IHL : ∀ t : list X,
          Some l = Some t → All2 (λ (x : option X) (y : X), x = Some y) L t
  ============================
   (All2 (λ (x : option X) (y : X), x = Some y) (Some x :: L) t)


DEBUG:Going to execute:
inversion_clear H