Goal:
  
  G : t
  s0 : VSet.t
  s' : VSet.t
  x : V.t
  y : V.t
  z : V.t
  d : DisjointAdd x s0 s'
  e : EdgeOf x y
  a : SPath s0 y z
  s1 : VSet.t
  x0 : V.t
  ============================
   (NoConfusion_SPath
      {|
        pr1 := {| pr1 := s'; pr2 := {| pr1 := x; pr2 := z |} |};
        pr2 := spath_step d e a
      |}
      {|
        pr1 := {| pr1 := s1; pr2 := {| pr1 := x0; pr2 := x0 |} |};
        pr2 := spath_refl s1 x0
      |} ->
    let H := CoreTactics.block in
    {|
      pr1 := {| pr1 := s'; pr2 := {| pr1 := x; pr2 := z |} |};
      pr2 := spath_step d e a
    |} =
    {|
      pr1 := {| pr1 := s1; pr2 := {| pr1 := x0; pr2 := x0 |} |};
      pr2 := spath_refl s1 x0
    |})


DEBUG:Going to execute:
CoreTactics.intros_until_block
DEBUG LTAC Evaluated term: (NoConfusion_SPath
                              {|
                                pr1 :=
                                  {|
                                    pr1 := s';
                                    pr2 := {| pr1 := x; pr2 := z |}
                                  |};
                                pr2 := spath_step d e a
                              |}
                              {|
                                pr1 :=
                                  {|
                                    pr1 := s1;
                                    pr2 := {| pr1 := x0; pr2 := x0 |}
                                  |};
                                pr2 := spath_refl s1 x0
                              |} ->
                            let H := CoreTactics.block in
                            {|
                              pr1 :=
                                {|
                                  pr1 := s'; pr2 := {| pr1 := x; pr2 := z |}
                                |};
                              pr2 := spath_step d e a
                            |} =
                            {|
                              pr1 :=
                                {|
                                  pr1 := s1;
                                  pr2 := {| pr1 := x0; pr2 := x0 |}
                                |};
                              pr2 := spath_refl s1 x0
                            |})