Goal:
    A : Type  P : list A → A → Type  x : A  a : All_fold P [x]
  ============================
   (P [] x)


DEBUG:Going to execute:
intro_block_id H || intro_block H
Level 0: Backtrace:

No quantified hypothesis named a in current goal even after head-reduction.
Level 0: Backtrace:

No quantified hypothesis named a in current goal even after head-reduction.