Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  x : V.t
  z : Z
  p : SPath G (V G) x (s G)
  ============================
   (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 cont =>
             DepElim.generalize_sig_gen id
              ltac:(fun id id' id'1 t =>
                      move_after_deps id' t; CoreTactics.revert_until id';
                       rename id' into id; cont id'1 id)