redef fun -(i) is intern

	redef fun -(i) is intern

	redef fun -(i) is intern

	redef fun -(i) is intern

	redef fun -(i) is intern

    #     assert("5/2".to_r - "3/2".to_r == 1.to_r)
    redef fun -(r) do
        var res = new NativeMPQ
        val.sub(res, r.val)
        return new Ratio(res)
    end

	redef fun -(i) is intern

	redef fun -(i) is intern

    #     assert(2.to_bi - 2.to_bi == 0.to_bi)
    redef fun -(i) do
        var res = new NativeMPZ
        val.sub(res, i.val)
        return new BigInt(res)
    end

	redef fun -(i) is intern