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


DEBUG:Going to execute:
elim id
Level 2: evaluation returns
<coq-core.plugins.tauto::is_conj@0>
where
tauto_flags := 
of type
tauto_flags
X1 := All P l × All Q l
of type
constr of type tacvalue