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
  ============================
   (let H := CoreTactics.block in
    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 H0 := 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:
change T; CoreTactics.intros_until_block
Level 5: T
 has value 
(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
 |})