interface I
{
  in void a();
  in void b();

  out void c();
  out void d();

  behaviour
  {
    bool f = false;

    void toggle ()
    {
      if (f)
      {
        c;
      }
      f = !f;
    }
    [true]
    {
      on a:
      {
	toggle();
      }
      on b:
      {
	toggle();
	toggle();
	d;
      }
    }
  }
}

component function
{
  provides I i;

  behaviour
  {
    bool f = false;

    void toggle ()
    {
      if (f)
      {
        i.c();
      }
      f = !f;
    }
    [true]
    {
      on i.a():
      {
	toggle();
      }
      on i.b():
      {
	toggle();
	toggle();
	i.d();
      }
    }
  }
}