Goal:
  
  T : Type -> Type
  M : Monad T
  A : Type
  P : nat -> A -> Type
  k : nat
  a : A
  l : list A
  f : forall (n : nat) (x : A),
      nth_error (a :: l) n = Some x -> T (∥ P (k + n) x ∥)
  ============================
   (Some a = Some a)


DEBUG:Going to execute:
try CoreTactics.solve_wf
Level 2: 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 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 2: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.