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
  a0 : SPath G s0 y z
  IHa0 : let H := CoreTactics.block in
         let H0 := CoreTactics.block in
         let H1 := CoreTactics.block in
         Acc
           (fun
              x
               y : sigma
                     (fun
                        index : sigma
                                  (fun _ : VSet.t =>
                                   sigma (fun _ : V.t => V.t)) =>
                      SPath G (pr1 index) (pr1 (pr2 index)) (pr2 (pr2 index)))
            =>
            SPath_direct_subterm G (pr1 (pr1 x)) (pr1 (pr2 (pr1 x)))
              (pr2 (pr2 (pr1 x))) (pr1 (pr1 y)) (pr1 (pr2 (pr1 y)))
              (pr2 (pr2 (pr1 y))) (pr2 x) (pr2 y))
           {|
             pr1 := {| pr1 := s0; pr2 := {| pr1 := y; pr2 := z |} |};
             pr2 := a0
           |}
  ============================
   (let H := CoreTactics.block in
    let H0 := CoreTactics.block in
    Acc
      (fun
         x
          y : sigma
                (fun
                   index : sigma
                             (fun _ : VSet.t => sigma (fun _ : V.t => V.t))
                 => SPath G (pr1 index) (pr1 (pr2 index)) (pr2 (pr2 index)))
       =>
       SPath_direct_subterm G (pr1 (pr1 x)) (pr1 (pr2 (pr1 x)))
         (pr2 (pr2 (pr1 x))) (pr1 (pr1 y)) (pr1 (pr2 (pr1 y)))
         (pr2 (pr2 (pr1 y))) (pr2 x) (pr2 y))
      {|
        pr1 := {| pr1 := s'; pr2 := {| pr1 := x; pr2 := z |} |};
        pr2 := spath_step G s0 s' x y z d e a0
      |})


DEBUG:Going to execute:
cbn beta in hyp; eqns_specialize_eqs_block hyp;
            cbn[eq_rect_r eq_rect] in hyp
Level 3: Backtrace:

Tactic failure: Nothing to do in hypothesis IHa0(let H := CoreTactics.block
                                                 in
                                                 Acc
                                                 (fun
                                                 x
                                                 y : 
                                                 sigma
                                                 (fun
                                                 index : 
                                                 sigma
                                                 (fun _ : VSet.t =>
                                                 sigma (fun _ : V.t => V.t))
                                                 =>
                                                 SPath G 
                                                 (pr1 index)
                                                 (pr1 (pr2 index))
                                                 (pr2 (pr2 index))) =>
                                                 SPath_direct_subterm G
                                                 (pr1 (pr1 x))
                                                 (pr1 (pr2 (pr1 x)))
                                                 (pr2 (pr2 (pr1 x)))
                                                 (pr1 (pr1 y))
                                                 (pr1 (pr2 (pr1 y)))
                                                 (pr2 (pr2 (pr1 y))) 
                                                 (pr2 x) 
                                                 (pr2 y))
                                                 {|
                                                 pr1 :=
                                                 {|
                                                 pr1 := s0;
                                                 pr2 :=
                                                 {| pr1 := y; pr2 := z |}
                                                 |};
                                                 pr2 := a0
                                                 |}).
Level 3: Backtrace:

Tactic failure: Nothing to do in hypothesis IHa0(let H := CoreTactics.block
                                                 in
                                                 Acc
                                                 (fun
                                                 x
                                                 y : 
                                                 sigma
                                                 (fun
                                                 index : 
                                                 sigma
                                                 (fun _ : VSet.t =>
                                                 sigma (fun _ : V.t => V.t))
                                                 =>
                                                 SPath G 
                                                 (pr1 index)
                                                 (pr1 (pr2 index))
                                                 (pr2 (pr2 index))) =>
                                                 SPath_direct_subterm G
                                                 (pr1 (pr1 x))
                                                 (pr1 (pr2 (pr1 x)))
                                                 (pr2 (pr2 (pr1 x)))
                                                 (pr1 (pr1 y))
                                                 (pr1 (pr2 (pr1 y)))
                                                 (pr2 (pr2 (pr1 y))) 
                                                 (pr2 x) 
                                                 (pr2 y))
                                                 {|
                                                 pr1 :=
                                                 {|
                                                 pr1 := s0;
                                                 pr2 :=
                                                 {| pr1 := y; pr2 := z |}
                                                 |};
                                                 pr2 := a0
                                                 |}).
Level 3: Backtrace:

Tactic failure: Nothing to do in hypothesis IHa0(let H := CoreTactics.block
                                                 in
                                                 Acc
                                                 (fun
                                                 x
                                                 y : 
                                                 sigma
                                                 (fun
                                                 index : 
                                                 sigma
                                                 (fun _ : VSet.t =>
                                                 sigma (fun _ : V.t => V.t))
                                                 =>
                                                 SPath G 
                                                 (pr1 index)
                                                 (pr1 (pr2 index))
                                                 (pr2 (pr2 index))) =>
                                                 SPath_direct_subterm G
                                                 (pr1 (pr1 x))
                                                 (pr1 (pr2 (pr1 x)))
                                                 (pr2 (pr2 (pr1 x)))
                                                 (pr1 (pr1 y))
                                                 (pr1 (pr2 (pr1 y)))
                                                 (pr2 (pr2 (pr1 y))) 
                                                 (pr2 x) 
                                                 (pr2 y))
                                                 {|
                                                 pr1 :=
                                                 {|
                                                 pr1 := s0;
                                                 pr2 :=
                                                 {| pr1 := y; pr2 := z |}
                                                 |};
                                                 pr2 := a0
                                                 |}).
Level 3: Backtrace:

Tactic failure: Nothing to do in hypothesis IHa0(let H := CoreTactics.block
                                                 in
                                                 Acc
                                                 (fun
                                                 x
                                                 y : 
                                                 sigma
                                                 (fun
                                                 index : 
                                                 sigma
                                                 (fun _ : VSet.t =>
                                                 sigma (fun _ : V.t => V.t))
                                                 =>
                                                 SPath G 
                                                 (pr1 index)
                                                 (pr1 (pr2 index))
                                                 (pr2 (pr2 index))) =>
                                                 SPath_direct_subterm G
                                                 (pr1 (pr1 x))
                                                 (pr1 (pr2 (pr1 x)))
                                                 (pr2 (pr2 (pr1 x)))
                                                 (pr1 (pr1 y))
                                                 (pr1 (pr2 (pr1 y)))
                                                 (pr2 (pr2 (pr1 y))) 
                                                 (pr2 x) 
                                                 (pr2 y))
                                                 {|
                                                 pr1 :=
                                                 {|
                                                 pr1 := s0;
                                                 pr2 :=
                                                 {| pr1 := y; pr2 := z |}
                                                 |};
                                                 pr2 := a0
                                                 |}).
Level 3: Backtrace:

Tactic failure: Nothing to do in hypothesis IHa0(let H := CoreTactics.block
                                                 in
                                                 Acc
                                                 (fun
                                                 x
                                                 y : 
                                                 sigma
                                                 (fun
                                                 index : 
                                                 sigma
                                                 (fun _ : VSet.t =>
                                                 sigma (fun _ : V.t => V.t))
                                                 =>
                                                 SPath G 
                                                 (pr1 index)
                                                 (pr1 (pr2 index))
                                                 (pr2 (pr2 index))) =>
                                                 SPath_direct_subterm G
                                                 (pr1 (pr1 x))
                                                 (pr1 (pr2 (pr1 x)))
                                                 (pr2 (pr2 (pr1 x)))
                                                 (pr1 (pr1 y))
                                                 (pr1 (pr2 (pr1 y)))
                                                 (pr2 (pr2 (pr1 y))) 
                                                 (pr2 x) 
                                                 (pr2 y))
                                                 {|
                                                 pr1 :=
                                                 {|
                                                 pr1 := s0;
                                                 pr2 :=
                                                 {| pr1 := y; pr2 := z |}
                                                 |};
                                                 pr2 := a0
                                                 |}).