Goal:
  
  A : Type
  H : ReflectEq A
  l1 : list A
  l2 : list A
  l : list A
  packcall := {| pr1 := l1; pr2 := l2 |} : sigma (λ _ : list A, list A)
  packcall_fn := {|
                   pr1 := packcall;
                   pr2 := split_prefix (pr1 packcall) (pr2 packcall)
                 |}
              : sigma
                  (λ _ : sigma (λ _ : list A, list A),
                     (list A * list A * list A)%type)
  ============================
   (packcall_fn =
    {|
      pr1 := {| pr1 := l1; pr2 := l2 |};
      pr2 :=
        split_prefix (pr1 {| pr1 := l1; pr2 := l2 |})
          (pr2 {| pr1 := l1; pr2 := l2 |})
    |}
    → let H := CoreTactics.block in
      is_prefix l l1
      → is_prefix l l2 → is_prefix l (fst (fst (split_prefix l1 l2))))


DEBUG:Going to execute:
refine (DepElim.eq_simplification_sigma1 _ _ _ _ _) ||
             refine (DepElim.eq_simplification_sigma1_nondep_dep _ _ _ _ _)
              || refine (DepElim.eq_simplification_sigma1_dep _ _ _ _ _)
DEBUG LTAC Evaluated term: (packcall_fn =
                            {|
                              pr1 := {| pr1 := l1; pr2 := l2 |};
                              pr2 :=
                                split_prefix (pr1 {| pr1 := l1; pr2 := l2 |})
                                  (pr2 {| pr1 := l1; pr2 := l2 |})
                            |}
                            → let H := CoreTactics.block in
                              is_prefix l l1
                              → is_prefix l l2
                                → is_prefix l
                                    (fst (fst (split_prefix l1 l2))))
Level 2: evaluation returns
idtac of type tacvalue