Modeling numbers with vectors of vectors?

Solution 1:

Your structure has big problems when you try to implement additive inverses $[-n]$ for $n\in\Bbb N$ with some reasonable porperties. E.g. using the natural assumption $[-1]\cdot[-1]=[1]$ will lead to a contradiction. Assume a representation

$$[-1]=\langle a_0,a_1,...\rangle.$$

The assumption then tells us that $a_i+a_i=0$. Because of distributivity, this is equivalent to $[2]a_i=0$. Assuming the further representation $a_i=\langle b_0^i,b_1^i,...\rangle$, we can deduce that

$$0=[2]a_i=\langle b_0^i+1,b_1^i,...\rangle\quad\Rightarrow\quad b_0^i+1=\omega,\quad b_j^i=\omega,j>1.$$

This means $a_i=\langle b_0^i,\omega^\infty\rangle$ for some strange corporeal numbers $b_0^i$ with $b_0^i+1=\omega$. But now you see

$$b_0^i=b_0^i+[0]=b_0^i+([1]+[-1])=(b_0^i+[1])+[-1]=\omega+[-1]=\omega.$$

This means that actually $a_i=\langle\omega^\infty\rangle=0$ and therefore $[-1]=[1]$. This is certainly unwanted. Even worse, as $[-1]$ by definition satisfies $[1]+[-1]=[0]$, we just proved $[2]=[0]$. This is a contradiction.

So what now? You do not seem to have additive inverses with some natural behavior. To implement mutliplicative inverses you need additive inverses. And to implement $[\pi]$ and other real numbers you certainly need one of the above as you already demonstrated.

Actually, the existence of this strange absorbing "hard zero" $\omega$ boggles me. I got the feeling the structure might be much more well behaved if we allowe the corporeal numbers to also be finite sequences and defining $[0]:=\langle\rangle$.

Solution 2:

This is an answer to the question as it was stated initially. There it seemed as if $\def\corpo{\Bbb C_{\text{orpo}}}\corpo$ should extend the natural numbers $\Bbb N$ in a certain way. Among other things, I assume the addition and multiplication of $\corpo$ to be distributive (the former axiom 4).

I thought a lot about this interesting construct and I found a purely algebraic formulation you are maybe interested in. Note that you cannot use the setbuilder notation in the way you did: you cannot use the defined set inside the braces on the right side. You might run into foundational problems with a too naive approach. So, if we cannot directly construct the corporeals this way, we at least can state (in an algebraic fashion) what we want them to be.

In the natural numbers we have the following kind of prime factorization: if $n\in\Bbb N\setminus\{0\}$ and $p_i$ is the $i$-th prime number, then there are unique $k_i\in\Bbb N$ (only finitely many are non-zero) so that

$$n=\prod_i p_i^{k_i}.$$

It now is natural to extend this in several ways:

• We want to allow infinitely many non-zero $k_i$, i.e. numbers with infinitely many different prime factors.
• We want to have exponents not only from $\Bbb N$ but from a more general appropriate space $R$. It would be exceptionally nice if the exponents come from the same space as the one we are currently defining.
• We do not want to have $0$ as an exception but we want it to have a unique factorization too.

Now let me show you how to express the fact that $\Bbb N$ allows a unique prime factorization in an algebraic way. First note that $(\Bbb N,+,\cdot)$ is a semiring, i.e. has associative, commutative addition with $0$; associative, distributive multiplication with $1$; $0$ is multiplicatively absorbing. The existence of a prime factorization now is equivalent to the existence of a specific isomorphism $\varphi$ between the additive and multiplicative strucuture of $\Bbb N$. More precisely, we want a monoid-isomorphism

$$\varphi :(\Bbb N\setminus\{0\},\cdot) \leftrightarrow (\Bbb N^{\Bbb N}_{\text{fin}},+).$$

Here, $(\Bbb N\setminus\{0\},\cdot)$ is the multiplicative monoid of $\Bbb N\setminus\{0\}$ (just the associative multiplication with $1$). $\Bbb N^{\Bbb N}_{\text{fin}}$ is the set of all sequences of natural numbers with only finitely many non-zero entries. Together with componentwise addition, this will give an additive monoid. This might seem strange at first, but is just your $\langle\cdot\rangle$ notation in disguise. E.g. if $n\in\Bbb N$ with prime factors $p_i^{k_i}$, then

$$n=\langle k_0,k_1,...\rangle=\prod_ip_i^{k_i} \qquad\Longleftrightarrow\qquad \varphi(n)=(k_0,k_1,...).$$

In still other words $\varphi(\langle k_0,k_1,...\rangle)=(k_0,k_1,...)$.

So why do I write this so complicated as an isomorphism? At first, isomorphisms are structure preserving, i.e. $\varphi(n\cdot m)=\varphi(n)+\varphi(m)$. This resembles your former componentwise addition axiom 3. On the other hand isomorphisms are bijective, hence this reflects the fact that a prime factorization is unique, and that any possible prime factorization gives us one unique natural number. All this is packed in only a few words and now one can apply the whole power of abstract algebra to deduce and generalize.

Now lets see where your corporeals can be placed in here. We are looking for a $\Bbb N$-extending semiring $(R,+,\cdot)$ with an even stronger connection between the additive and multiplicative structure, namely we claim the existence of a monoid-isomorphism

$$\varphi:(R,\cdot)\leftrightarrow(R^{\Bbb N},+).$$

Note the following:

• We have used $R$ instead of $R\setminus\{0\}$ on the left, hence we expect that also the zero $0$ has a unqiue prime factorization.
• We have removed the $\text{fin}$ from the right side, so we allow a factorization of a number $n\in R$ to contain infinitely many different primes.
• We have used $R$ on the right instead of only $\Bbb N$, hence our exponents can be all numbers from this newly defined space. This automatically equips our space with an operation of exponentiation.

The question now is, whether such a semiring exists. If one exists we can call it $\corpo$ and take $\Bbb N$ as a specific sub-semiring. Actually you claimed one more thing for $\corpo$ to hold. Above definition says that any number $n\in R$ has a unique prime factorization with exponents in $R$. But we never stated what those primes are. If we specifically want the primes to be the prime numbers from $\Bbb N$, then we have to include the following further axiom: For $p_i\in\Bbb N$ being the $i$-th prime number, we claim

$$\varphi(p_i)=(\overbrace{0,...,0}^{i-1},1,0,0,...).$$

This makes $\varphi(p_i)$ a generating system of $(\corpo^{\Bbb N},+)$. If we do not claim this, it could happen that the former prime numbers are no longer prime in the extended space, but now are composites of new strange corporeal primes. We then cannot be sure that e.g. $\varphi(2)=(1,0,0,...)$. So we claimed it for convenience.

Here are some first observations. Lets begin with the cardinality of $\corpo$. As isomorphisms are bijective, this means that $\corpo$ and $\corpo^{\Bbb N}$ are of the same cardinality. But we have

$$|\Bbb N|^{|\Bbb N|}=|\Bbb R|\qquad \text{but}\qquad |\Bbb R|^{|\Bbb N|}=|\Bbb R|.$$

We therefore see that $\corpo$ must be uncountable. And this is not because it contains representations of all real numbers (you can see that it does not from my other answer), but only generalized integers. This means that it does contain many non-natural numbers.

I have never mentioned your "hard-zero" $\omega$ until now. This is because its existence follows naturally from the fact that we need a prime factorization of $0$. As $0$ is multiplicatively absorbing, the existence of $\varphi$ imples the existence of an additively absorbing element $\omega$ and

$$\varphi(0)=(\omega,\omega,...).$$