Goal:
  
  G1 : t
  G2 : t
  on_edge : forall x y : V.t, EdgeOf G1 x y -> EdgeOf G2 x y
  weight_on_edge : forall (x y : V.t) (e : EdgeOf G1 x y),
                   (on_edge x y e).π1 <= e.π1
  s : VSet.t
  x : V.t
  y : V.t
  p : SPath G1 s x y
  ============================
   (sweight (map_spath p) <= sweight p)


DEBUG:Going to execute:
unshelve refine_ho elimc
Level 8: evaluation returns
unshelve refine_ho elimc; cbv beta
where
elimt := fun_elim _ _ _
of type
uconstr
elimn := 3%nat
of type
constr
elimfn := @map_spath
of type
constr
elimc := fun_elim _ _ _ s x y p
of type
uconstr
c := map_spath p
of type
constr of type tacvalue