Goal:
  
  A : Type
  P : A → Type
  Q : A → Type
  x : A
  l : list A
  p : P x
  X : All P l
  IHX : All (λ x : A, P x → Q x) l → All Q l
  X0 : All (λ x : A, P x → Q x) (x :: l)
  x0 : A
  l0 : list A
  X2 : All (λ x : A, P x → Q x) l
  H0 : x0 = x
  H1 : l0 = l
  X3 : Q x
  ============================
   (All Q l)


DEBUG:Going to execute:
F x2 x1 x0
Level 2: evaluation returns
<coq-core.plugins.tauto::find_cut@0>
where
k := fun id0 id1 X2 => assert X2; [ exact (id0 id1) | clear id0 ]
     where
     flags := 
     of type
     tauto_flags
of type
tacvalue of type tacvalue