# Addition of 1 in Golden Mean Number System

## Algorithm

Let $x \in \R$ be a real number.

The following algorithm performs the operation of addition of $1$ to $x$ in the golden mean number system.

Let $S$ be the representation of $x$ in the golden mean number system in its simplest form.

Step $1$: Is the digit immediately to the left of the radix point a zero?
If Yes, replace that $0$ with $1$. Go to Step $4$.
If No, set $m = 2$ and go to Step $2$.

Step $2$: Does the $m$th place after the radix point contain $0$?
If Yes, expand the $100$ in the $3$ places ending in the $m$th place with $011$. Subtract $2$ from $m$. Go to Step $3$.
If No, add $2$ to $m$. Repeat Step $2$.

Step $3$: Is $m = 0$?
If Yes, set the digit immediately to the left of the radix point from $0$ to $1$. Go to Step $4$.
If No, go to Step $2$.

Step $4$: Convert $S$ to its simplest form. Stop.

## Proof

The above constitutes an algorithm, for the following reasons:

### Finiteness

The only case in which it is possible for the process not to terminate is if the $m$th place never contains $0$.

This can only happen if $S$ ends in an infinite string $01010101 \ldots$

But if this is the case, $S$ is not in its simplest form.

### Definiteness

Each step can be seen to be precisely defined.

### Inputs

The only input to the algorithm is the representation $S$ of $x$.

### Outputs

The only output from the algorithm is the representation $S$ of $x + 1$.

All operations that change $S$ are of the following nature:

$(1): \quad$ Simplification of $S$, which does not change $x$, which happens if at all in Step $4$.
$(2): \quad$ Expansion of $S$, which does not change $x$, which happens if at all in Step $2$.
$(3): \quad$ Setting the digit corresponding to $\phi^0$ to $1$ from $0$, which happens either in Step $1$ or in Step $3$.
In either step, it happens only once, after which the algorithm terminates.

### Effective

Each step is basic enough to be done exactly and predictably.

$\blacksquare$