Goal:
    G1 : t  G2 : t
  ============================
   (forall (s : VSet.t) (x y : V.t) (p : SPath G2 s x y),
    first_in_graph s x y p (first_in p))


DEBUG:Going to execute:
let eos := fresh "eos" in
           pose proof CoreTactics.the_end_of_the_section as eos