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


DEBUG:Going to execute:
try intros until H; intro_block_id H || intro_block H
Level 1: evaluation returns
try intros until H; intro_block_id H || intro_block H;
 (try simpl in H; DepElim.simplify_equations_in H)
where
H := a
of type
ident of type tacvalue