# Patent val/Properties

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This page shows some properties of patent vals as well as generalized patent vals (GPVs), although currently it is all about the latter.

## To tell if a val is a GPV

Suppose we have a p-limit val V, to tell if it is a GPV:

For every prime q in the p-limit, solve

$\displaystyle \operatorname {round} (n \log_2 q) = v_{\pi (q)}$

for n. The solution is

$\displaystyle \frac {v_{\pi (q)} - 1/2}{\log_2 (q)} \lt n \lt \frac {v_{\pi (q)} + 1/2}{\log_2 (q)}$

Let N1, N2, …, Nπ (p) denote the solution sets. Find

$\displaystyle \mathrm {N} = \bigcap_{i = 1}^{\pi (p)} \mathrm {N}_i$

Then V is a GPV of every edo in N if N is non-empty and not a singleton (i.e. a single point); otherwise it is not a GPV.

## Cardinality

Given a finite prime limit, the set of all GPVs are countably infinite.

## Sorting property

Given a finite prime limit, the set of all GPVs can be ordered in this way such that all but one entry in the GPV Vk and its next GPV Vk + 1 are the same, and for the different entry, the latter increments the former by 1.

This property states that, for example, if it is known that 12 19 28] is a GPV, then the next GPV is one of 13 19 28], 12 20 28], or 12 19 29].

This also holds for any rationally independent subgroups, such as 2.3.7 and 2.9.7, and even some rationally dependent subgroups, such as 2.3.9.7. It does not hold, however, for other rationally dependent subgroups, such as 2.3.27.7, where at certain points of edo number n, both the mappings for 3 and 27 increment.

Proof

By definition, the p-limit GPV of n-edo is V (n) = round (n log2 (Q)), where Q is the prime basis 2 3 5 … p].

The sorting property is equivalent to

1. for any prime qi in Q, there is a point of n to cause vi to increment to vi + 1; and
2. for any distinct primes qi, qj in Q, there is not a point of n to cause both vi and vj to increment to vi + 1 and vj + 1, respectively;

where an increment of f (x) at x0 is defined as lim xx0+ f (x) = lim xx0- f (x) + 1.

#1 holds immediately following the definition of the round function, and the point is n = (vi + 1/2)/log2 (qi).

To prove #2, let us assume there exists such an n. By the definition of the round function, an increment of y = round (x) occurs only if 2xZ. Thus, for any distinct primes qi, qj in Q, 2n log2 (qi) ∈ Z, and 2n log2 (qj) ∈ Z. If that is the case, then their quotient (2n log2 (qi))/(2n log2 (qj)) = logqj (qi) ∈ Q, which contradicts Gelfond–Schneider theorem. Therefore, the hypothesis is false, and such an n does not exist.

## Application

Given a finite prime limit, the above properties offer a way to iterate through all GPVs. To roll forwards:

1. Enter a GPV. Set i = 1.
2. Copy the input and increment its i-th entry by 1.
3. Test if it is a GPV.
4. If it is, return it and back to step 1; otherwise, increment i by 1 and back to step 2.

To roll backwards:

1. Enter a GPV. Set i = 1.
2. Copy the input and decrement its i-th entry by 1.
3. Test if it is a GPV.
4. If it is, return it and back to step 1; otherwise, increment i by 1 and back to step 2.

Notice that the all-zero val is a GPV, you can always enter it for the first one. It is guaranteed that you can iterate through all GPVs in this method. In practice it is recommended to start with the last entry and going backwards in step 2 for better performance, because the largest prime is most likely to increment.