Goal:
  
  A : Type
  B : Type
  R : A → B → Type
  R' : ∀ (a : A) (b : B), R a b → Type
  b : All2_dep R' All2_nil
  b0 := {|
          pr1 := {| pr1 := []; pr2 := {| pr1 := []; pr2 := All2_nil |} |};
          pr2 := b
        |}
     : sigma
         (λ index : sigma
                      (λ xs : list A, sigma (λ ys : list B, All2 R xs ys)),
            All2_dep R' (pr2 (pr2 index)))
  ============================
   (let H := CoreTactics.block in
    NoConfusionHom_All2_dep A B R R' [] [] All2_nil All2_dep_nil b
    → let H0 := CoreTactics.block in All2_dep_nil = b)


DEBUG:Going to execute:
lazymatch goal with
           | id':=?v:_
             |- context [ id ] =>
                 generalize (eq_refl : v = id'); clearbody id'; simpl in id';
                  cont id id' id v
           | id':=?v:_
             |- _ =>
                 let id'1 := fresh id' in
                 let id'2 := fresh id' in
                 set (id'2 := pr2 id'); set (id'1 := pr1 id') in id'2;
                  hnf in (value of id'1), (value of id'2);
                  try red in (type of id'2);
                  match goal with
                  | id'1:=?t:_
                    |- _ =>
                        generalize (eq_refl : t = id'1); clearbody id'2 id'1;
                         clear id' id; try unfold signature in id'2;
                         hnf in id'2; simpl in id'2; rename id'2 into id;
                         cont id id id'1 t
                  end
           end