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) × All Q (x :: l))


DEBUG:Going to execute:
assert X2
Level 1: evaluation returns
assert X2; [ exact (id0 id1) | clear id0 ]
where
id1 := x
of type
intropattern
id0 := P
of type
intropattern
flags := 
of type
tauto_flags
X2 := Type
of type
constr of type tacvalue