Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  y_0 : V.t
  x_0 : V.t
  Vx : VSet.In x_0 (V G)
  Vy : VSet.In y_0 (V G)
  K : Z
  Hxs : lsp G x_0 y_0 = Some K
  e : EdgeSet.elt
  He : e = (y_0, - K, x_0) \/ EdgeSet.In e (E G)
  ============================
   (VSet.In e..s (V G) /\ VSet.In e..t (V G))


DEBUG:Going to execute:
destruct He as [He| He]
DEBUG LTAC Evaluated term: EdgeSet.add_spec