Goal:
  
  A : Type
  B : Type
  P : A → nat → B → Type
  a : A
  ls2 : list A
  n : nat
  X : Alli (λ (n : nat) (y : B), All (λ x : A, P x n y) (a :: ls2)) n []
  ============================
   (All (λ x : A, Alli (P x) n []) ls2)


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