# Modulo of `self` with `i`.
    #
    # Finds the remainder of the division of `self` by `i`.
    #
    #     assert(5.to_bi % 2.to_bi == 1.to_bi)
    fun %(i: BigInt): BigInt do
        var res = new NativeMPZ
        val.mod(res, i.val)
        return new BigInt(res)
    end