Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  p0 : sigma
         (fun index : sigma (fun _ : VSet.t => sigma (fun _ : V.t => V.t)) =>
          SPath G (pr1 index) (pr1 (pr2 index)) (pr2 (pr2 index)))
  x : V.t
  z : Z
  p : SPath G (V G) x (s G)
  ============================
   ({|
      pr1 := {| pr1 := V G; pr2 := {| pr1 := x; pr2 := s G |} |}; pr2 := p
    |} = p0 ->
    let H := CoreTactics.block in
    sweight p = z ->
    ~ VSet.In x (V G) -> let H0 := CoreTactics.block in z = 0)


DEBUG:Going to execute:
fun id =>
             CoreTactics.on_last_hyp
              ltac:(fun id' =>
                      match id' with
                      | id => idtac
                      | _ => revert id'; CoreTactics.revert_until id
                      end)