}
    }

    @Test
    fun `Peano sanity check`() {

        assertThat(
            Peano.fromInt(0),
            equalTo(Peano.Z)
        )

        assertThat(
            Peano.fromInt(1024).toInt(),
            equalTo(1024)
        )
    }

    sealed class Peano {

        companion object {

            fun fromInt(n: Int): Peano = (0 until n).fold(Z as Peano) { acc, _ -> S(acc) }