interface IfaceA : Object {
    public abstract void method_a ();
}

interface IfaceB : Object, IfaceA {
    public abstract void method_b ();
}

class Demo : Object, IfaceA, IfaceB {
    public void method_a () { stdout.printf ("a called\n"); }
    public void method_b () { stdout.printf ("b called\n"); }
    public void method_c () { stdout.printf ("c called\n"); }

    static int main ()
      {
        stdout.printf ("Hello world!\n");
        var demo = new Demo ();
        demo.method_a ();
        demo.method_b ();
        demo.method_c ();
        return 0;
      }
}