public struct Peano
{
    public delegate Peano AppPeano();
    public AppPeano? appPeano;

    public Peano(AppPeano? appPeano)
    {
        this.appPeano = appPeano;
    }

    public static Peano halt = new(null);
    public static Peano Iter(Peano peano)
    {
        return new(() => peano);
    }

    public static Peano omega = Iter(omega);
}

public struct Peano
{
    public delegate Peano AppPeano();
    public AppPeano? appPeano;

    public Peano()
    {
        appPeano = null;
    }

    public Peano(Peano peano)
    {
        appPeano = () => peano;
    }

    public static Peano omega = new(omega);
}