Goal:
  
  A : Type
  P : A → Type
  Q : A → Type
  x : A
  l : list A
  X : All (λ x : A, P x × Q x) l
  a : P x
  b : Q x
  a0 : All P l
  b0 : All Q l
  ============================
   (All P (x :: l))


DEBUG:Going to execute:
<Coq.Init.Tauto.is_empty> flags X1; elim H
Level 3: evaluation returns
<coq-core.plugins.tauto::is_unit_or_eq@0>
where
tauto_flags := 
of type
tauto_flags
X1 := All P (x :: l)
of type
constr of type tacvalue

Level 3: Backtrace:

Tactic failure.
Level 3: Backtrace:

Tactic failure.
Level 2: Backtrace:

Tactic failure.
Level 2: Backtrace:

Tactic failure.