Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  p' : sigma (fun _ : VSet.t => sigma (fun _ : V.t => V.t))
  p : SPath G (pr1 p') (pr1 (pr2 p')) (pr2 (pr2 p'))
  ============================
   (forall (x : V.t) (z : Z) (p0 : SPath G (V G) x (s G)),
    {|
      pr1 := {| pr1 := V G; pr2 := {| pr1 := x; pr2 := s G |} |}; pr2 := p0
    |} = {| pr1 := p'; pr2 := p |} ->
    let H := CoreTactics.block in
    sweight p0 = z ->
    ~ VSet.In x (V G) -> let H0 := CoreTactics.block in z = 0)


DEBUG:Going to execute:
let xn := fresh id "'" in
           destruct id as [xn id]; DepElim.decompose_exists xn id;
            cbv beta iota delta [TODO projection TODO projection] in id, id';
            DepElim.decompose_exists id id'
DEBUG LTAC Evaluated term: p'
DEBUG LTAC Evaluated term: (sigma
                              (fun _ : VSet.t => sigma (fun _ : V.t => V.t)))
Level 3: type of id
 has value 
(sigma (fun _ : VSet.t => sigma (fun _ : V.t => V.t)))