Goal:
  
  G : t
  s0 : VSet.t
  s' : VSet.t
  x : V.t
  y : V.t
  z : V.t
  d : DisjointAdd x s0 s'
  e0 : EdgeOf x y
  a : SPath s0 y z
  s1 : VSet.t
  x0 : V.t
  e : False
  ============================
   (noConfusion_SPath_obligation_2
      {|
        pr1 := {| pr1 := s'; pr2 := {| pr1 := x; pr2 := z |} |};
        pr2 := spath_step d e0 a
      |}
      {|
        pr1 := {| pr1 := s1; pr2 := {| pr1 := x0; pr2 := x0 |} |};
        pr2 := spath_refl s1 x0
      |}
      (noConfusion_SPath_obligation_1
         {|
           pr1 := {| pr1 := s'; pr2 := {| pr1 := x; pr2 := z |} |};
           pr2 := spath_step d e0 a
         |}
         {|
           pr1 := {| pr1 := s1; pr2 := {| pr1 := x0; pr2 := x0 |} |};
           pr2 := spath_refl s1 x0
         |} e) = e)


DEBUG:Going to execute:
match type of H with
           | ?R ?x ?y =>
               let rhs := fresh in
               set (rhs := y) in *; pattern sigma rhs; clearbody rhs;
                destruct H; simpl
           end