interface iguardif {
  in void e();
  out void a();
  out void b();
  out void x();
  behaviour {
    on e: a;
    on e: {}
    on e: b;
  }
}

component guardif {
  provides iguardif p;
  behaviour {
    bool b = false;
    on p.e(): {
      [b]
        if (false) {
          if (false)
            p.x();
        }
      [!b] { b = true; p.a(); }
    }
  }
}