# Notation for function $+ \rightarrow \times$

Is there a standard notation to represent the function building the multiplication from the addition (I'm talking of the usual $+$ on $\Bbb N$)?

I'm tempted by: $$x \times y = + ^ y (x)$$

With such a notation I'd like to write: $$x ^ y = \times ^ y (x)$$

Is there any standard notation to represent this building relationship: $$\epsilon: + \rightarrow \times$$

This is not a complete answer

This relation can be formalized as definition by recursion:

if we can create an infinite sequence of binary operation on $\Bbb N$ in this way:

First we define $+_1:=+$

we can define $+_{k+1}$ from $+_{k}$ using the recursion over naturals with three steps.

$i)\,\,\,\, m +_{k+1} 0= b_{k+1}$

$ii)\,\,\,\, m +_{k+1}(n+1)=m+_k (m +_{k+1}n)$

$iii)\,\,\,\, b_ {n+1}:= \begin{cases} b, & \text{if$n=0$} \\ 0, & > \text{if$n=1$} \\ 1, & \text{if$n\gt 1$} \\ \end{cases}$

In this way we can go from $+_{k}$ to $+_{k+1}$.

This is the same way we build the Hyperoperations (see here)

$i)\,\,\,\, H_0(a,b):=S(b)=b+1$

$ii)\,\,\,\,H_{n+1}(a,0):=a_{n+1}$

$iii)\,\,\,\,H_{n+1}(a,b+1):=H_n(a,H_{n+1}(a,b))$

$iv)\,\,\,\, a_ {n+1}:= \begin{cases} a, & \text{if$n=0$} \\ 0, & > \text{if$n=1$} \\ 1, & \text{if$n\gt 1$} \\ \end{cases}$

As we can see your $\epsilon$ has this property

$$\epsilon (+_{k})=+_{k+1}$$

About such $\epsilon$ that in our case it takes a binary operation as a imput and give a binary operation as output but I never saw it. Instead I saw a similar concept for unary fucntions called Superfunction.

We call $F$ superfunction (related with Abel Functions) the solution of the functional equation

$$F(0)=b$$

$$F(n+1)=h(F(n))$$

Q I don't know if there is a notation for this solution but I am interested to know if there is a standard one.

I usually write $F$, the solution of this equation, as $\mathcal S [h]$: $$F=\mathcal S [h]$$

$$\mathcal S [h](n+1)=h(\mathcal S [h](n))$$

because I saw it somewhere but I don't remember where.

So if we use this notation for our operations turning them in to unary functions for a fixed $b$

$f_0(n):=H_0(b,n)=n+1$

$f_k(n):= H_k(b,n)=b +_{k} n$

we can find that $f_{k+1}(n):= H_{k+1}(b,n)=b +_{k+1} n$ is the Superfunction of $f_{k}(n)$

so where $f_1(n)=b +_{1} n=b+ n$ we have

$$\mathcal S [f_1](n)=f_2(n)=b +_{2} n=b\times n$$

and in general

$$\mathcal S [f_{k}]=f_{k+1}$$

I do not claim that this is good notation, but if you want to use standard notation to express this relationship, you can use $$x\times y=(\bullet+x)^y(0) .$$ Others might write $\lambda z.z+x$ instead of $\bullet+x$.

• Dear down-voter, if you do not understand, you can ask, if you have objections, you can voice them. – Carsten S Jan 6 '14 at 17:03