Goal:
  
  G : t
  s0 : VSet.t
  x : V.t
  s1 : VSet.t
  s' : VSet.t
  x0 : V.t
  y : V.t
  z : V.t
  d : DisjointAdd x0 s1 s'
  e : EdgeOf x0 y
  b : SPath s1 y z
  ============================
   (let H := CoreTactics.block in
    NoConfusion_SPath
      {|
        pr1 := {| pr1 := s0; pr2 := {| pr1 := x; pr2 := x |} |};
        pr2 := spath_refl s0 x
      |}
      {|
        pr1 := {| pr1 := s'; pr2 := {| pr1 := x0; pr2 := z |} |};
        pr2 := spath_step d e b
      |} ->
    let H0 := CoreTactics.block in
    {|
      pr1 := {| pr1 := s0; pr2 := {| pr1 := x; pr2 := x |} |};
      pr2 := spath_refl s0 x
    |} =
    {|
      pr1 := {| pr1 := s'; pr2 := {| pr1 := x0; pr2 := z |} |};
      pr2 := spath_step d e b
    |})


DEBUG:Going to execute:
change T; CoreTactics.intros_until_block
Level 5: T
 has value 
(NoConfusion_SPath
   {|
     pr1 := {| pr1 := s0; pr2 := {| pr1 := x; pr2 := x |} |};
     pr2 := spath_refl s0 x
   |}
   {|
     pr1 := {| pr1 := s'; pr2 := {| pr1 := x0; pr2 := z |} |};
     pr2 := spath_step d e b
   |} ->
 let H := CoreTactics.block in
 {|
   pr1 := {| pr1 := s0; pr2 := {| pr1 := x; pr2 := x |} |};
   pr2 := spath_refl s0 x
 |} =
 {|
   pr1 := {| pr1 := s'; pr2 := {| pr1 := x0; pr2 := z |} |};
   pr2 := spath_step d e b
 |})