Goal:
  
  G1 : t
  G2 : t
  l : labelling
  Gl := relabel_on G1 G2 l : t
  H : invariants G1
  preserves_edges : forall e : EdgeSet.elt,
                    EdgeSet.In e (E G1) -> EdgeSet.In e (E G2)
  HGl : correct_labelling G1 l
  H0 : invariants G2
  H1 : acyclic_no_loop G2
  embed : forall v1 v2 : VSet.elt,
          VSet.In v1 (V G1) ->
          VSet.In v2 (V G1) -> (lsp G2 v1 v2 <= lsp G1 v1 v2)%nbar
  G : t
  s0 : VSet.t
  s' : VSet.t
  x : V.t
  y : V.t
  z : V.t
  d : DisjointAdd x s0 s'
  e : EdgeOf G x y
  p0 : SPath G s0 y z
  x1 : V.t
  p1 : SPath G s0 x1 z
  H2 : DisjointAdd x s0 s'
  H3 : EdgeOf G x x1
  H4 : {|
         pr1 := s';
         pr2 :=
           {|
             pr1 := x;
             pr2 :=
               {|
                 pr1 := y;
                 pr2 :=
                   {|
                     pr1 := z;
                     pr2 := {| pr1 := d; pr2 := {| pr1 := e; pr2 := p0 |} |}
                   |}
               |}
           |}
       |} =
       {|
         pr1 := s';
         pr2 :=
           {|
             pr1 := x;
             pr2 :=
               {|
                 pr1 := x1;
                 pr2 :=
                   {|
                     pr1 := z;
                     pr2 :=
                       {| pr1 := H2; pr2 := {| pr1 := H3; pr2 := p1 |} |}
                   |}
               |}
           |}
       |}
  ============================
   (let H := CoreTactics.block in
    let H0 := CoreTactics.block in
    {| pr1 := {| pr1 := s0; pr2 := {| pr1 := y; pr2 := z |} |}; pr2 := p0 |} =
    {| pr1 := {| pr1 := s0; pr2 := {| pr1 := x1; pr2 := z |} |}; pr2 := p1 |})


DEBUG:Going to execute:
match goal with
           | |- context [ eq_rect_r _ _ eq_refl ] => progress simpl eq_rect_r
           | |- context [ eq_rect _ _ _ _ eq_refl ] => progress simpl eq_rect
           | |- context [ Prop.Logic.transport _ eq_refl _ ] =>
                 progress simpl Prop.Logic.transport
           | |- context [ Logic.eq_elim _ _ _ _ _ eq_refl ] =>
                 progress simpl eq_rect
           | |- context [ Logic.eq_elim_r _ _ _ _ eq_refl ] =>
                 progress simpl Logic.eq_elim_r
           | |- context [ noConfusion_inv _ ] =>
                 progress simpl noConfusion_inv
           | |- DepElim.opaque_ind_pack_eq_inv ?G eq_refl =>
                 apply (DepElim.simplify_ind_pack_inv B x p G)
           | |- let _ := CoreTactics.block in _ => fail 1
           | |- _ => simplify * || simplify ?; cbv beta
           | |- _ -> ?B =>
                 let ty := type of B in
                 intro || (let H := fresh in
                           intro
                           H)
           | |- forall x, _ => let H := fresh x in
                               intro
                               H
           | |- _ => intro
           end