Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  b : bool
  H : b -> False
  ============================
   (is_true (~~ b))


DEBUG:Going to execute:
fun tauto_flags X1 X2 id =>
             <coq-core.plugins.tauto::flatten_contravariant_conj@0>