Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  b : bool
  H : is_true (~~ b)
  H0 : is_true b
  ============================
   False


DEBUG:Going to execute:
match reverse goal with
           | |- ?X1 => <Coq.Init.Tauto.is_unit_or_eq> flags X1; constructor 1
           | H:?X1 |- _ => <Coq.Init.Tauto.is_empty> flags X1; elim H
           | _ => Ltac.assumption
           end