Goal:
    G1 : t  ext : EdgeSet.t  x : VSet.elt  e : Edge.t  s : VSet.t
  ============================
   (x = e..s /\ VSet.In x (V G1) \/
    x = e..t /\ VSet.In x (V G1) \/ VSet.In x s <->
    (x = e..s \/ x = e..t) /\ VSet.In x (V G1) \/ VSet.In x s)


DEBUG:Going to execute:
split
DEBUG LTAC Evaluated term: add_from_orig_spec
DEBUG LTAC Evaluated term: add_from_orig_spec
DEBUG LTAC Evaluated term: add_from_orig_spec