Goal:
  
  f : Edge.t -> Edge.t
  es : EdgeSet.t
  e : EdgeSet.elt
  x : Edge.t
  __view_subject_1_ : EdgeSet.In x es
  ============================
   (exists e0 : Edge.t, f x = f e0 /\ EdgeSet.In e0 es)


DEBUG:Going to execute:
exists x
DEBUG LTAC Evaluated term: InA_In_eq
DEBUG LTAC Evaluated term: (iffRL (P:=InA eq x (EdgeSetProp.to_list es))
                              (InA_In_eq x (EdgeSetProp.to_list es))
                              _view_subject_)
DEBUG LTAC Evaluated term: EdgeSet.elements_spec1
DEBUG LTAC Evaluated term: (iffLR (Q:=EdgeSet.In x es)
                              (EdgeSet.elements_spec1 es x)
                              (iffRL (P:=InA eq x (EdgeSetProp.to_list es))
                                 (InA_In_eq x (EdgeSetProp.to_list es))
                                 _view_subject_))