Goal:
  
  z : t
  hd : A.t
  tl : list A.t
  hd' : A.t
  tl' : list A.t
  H : A.lt hd hd'
  H' : lt (hd' :: tl') z
  ============================
   (lt (hd :: tl) z)


DEBUG:Going to execute:
PTRDEBUGTACtry 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 := H'
of type
ident of type tacvalue