Goal:
    G : t  x : V.t  i : V.t  source_vertex0 : VSet.In (s G) (V G)
  ============================
   True


DEBUG:Going to execute:
constructor 1
Level 6: evaluation returns
<coq-core.plugins.tauto::is_unit_or_eq@0>
where
tauto_flags := 
of type
tauto_flags
X1 := True
of type
constr of type tacvalue