redef fun to_r do return self

    redef fun to_r do
        var tmp = new NativeMPQ
        tmp.set_d self
        return new Ratio(tmp)
    end

    #     assert(123.to_bi.to_r == 123.to_r)
    redef fun to_r do
        var tmp = new NativeMPQ
        tmp.set_z val
        return new Ratio(tmp)
    end

    redef fun to_r do
        var tmp = new NativeMPQ
        tmp.set_si(self, 1)
        return new Ratio(tmp)
    end