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:
try arith_congr
Level 0: Backtrace:

No product even after head-reduction.
Level 0: Backtrace:

No product even after head-reduction.
Level 3: Backtrace:

No product even after head-reduction.
Level 2: Backtrace:

No product even after head-reduction.
Level 1: Backtrace:

No product even after head-reduction.
Level 0: Backtrace:

No product even after head-reduction.
Level 0: Backtrace:

No product even after head-reduction.