Goal:
    A : Type  P : list A → A → Type  H : True
  ============================
   (All_fold_nil P = All_fold_nil P)


DEBUG:Going to execute:
intro_block_id H || intro_block H
Level 4: Backtrace:

No quantified hypothesis named H in current goal even after head-reduction.
Level 4: Backtrace:

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