Goal:
    G : t
  ============================
   (forall (s1 s' : VSet.t) (x0 y0 z : V.t),
    SPath s1 x0 y0 ->
    forall (s s0 : VSet.t) (x y z' : V.t),
    DisjointAdd x s s0 ->
    EdgeOf x y ->
    SPath s y z' ->
    Disjoint s0 s' ->
    SPath s' z' z -> DisjointAdd x (VSet.union s s') (VSet.union s0 s'))


DEBUG:Going to execute:
Tactics.program_simplify; try typeclasses eauto  10 with program