Goal:
  
  z : t
  hd : A.t
  tl : list A.t
  hd' : A.t
  tl' : list A.t
  H : A.lt hd hd'
  H'1 : sigma (fun _ : t => t)
  H' : lt_ (pr1 H'1) (pr2 H'1)
  ============================
   ({| pr1 := hd' :: tl'; pr2 := z |} = H'1 ->
    let H := CoreTactics.block in
    let H0 := CoreTactics.block in lt (hd :: tl) z)


DEBUG:Going to execute:
try rename id into id',id' into id
Level 3: evaluation returns
try rename id into id',id' into id; cont id'1 id
where
t := {| pr1 := hd' :: tl'; pr2 := z |}
of type
constr
id'1 := H'1
of type
constr
id' := H'
of type
ident
id := H'
of type
ident
cont := fun id id' => DepElim.decompose_exists id id'
        where
        id := H'
        of type
        ident
of type
tacvalue of type tacvalue