*Newer version: R function v2.0.1*

R function II is the second version of R function. It's not an extension of original R function.

## Contents

## Definition

### Syntax

The syntax of R function II is nRS, where -

- n is a positive integer, here called "base number"
- R is a symbol for the function
- S is a string made up of lbrace ("{"), rbrace with left-superscript "+m" (here m is a non-negative integer) (i.e. "
^{+m}}")and non-negative integers; S must suit these properties shown below:

- In any part of S, the nested level must be greaterequal to 0, and the end of S must has nested level 0
- In S, the rbrace of any brace mustn't be immediately after the lbrace of that brace
- We call a brace separator iff the superscript of it is "+m" with m > 0. In S, there must be a number or a brace not separator immediately after the lbrace or the rbrace of any separator

And there're some shorthands:

- The left-superscript "+0" can be omitted, and the left-superscript "+1" can be written as "+".
- {0
^{+1}} can be also written as a comma.

### Main process

Scan and apply rules. Case A1, A2, A3, B1 and B2 are terminal, but A4, B3 and C are not. After you apply a terminal rule, you'll return here, then you can choose any R to start scanning.

Scanning starts at the R symbol. Scan from left to right. There're 3 kinds of things we scan - 0, non-0 numbers and braces not a separator. Before scanning, set s = 1, and save the whole string to A_{1} (that's for case A3).

- Case A: If there's a 0,

- Case A1: If nothing is after it(or an R symbol immediately after it, this also mark the end), then apply \(nR0=2^n\). And return.
- Case A2: If a simple rbrace (m=0, or no +m's for shorthand) is immediately after it, that means the brace is equvalent to {0}. So change it into number 1. And return.
- Case A3: If an rbrace with +m's (m > 0) is immediately after it, that means the whole brace is the standard m-separator \(\{0^{+m}\}\).

- Let S
_{s}= \(\{0^{+m}\}\), set t = s - Repeat this:
- Subtract t by 1
- Let S
_{t}be the brace such that "nested level of S_{t}= nested level of S_{t+1}- 1" and "S_{t+1}is inside S_{t}" - If t = 1, then break the repeating, or else continue repeating.

- Set k = m, s(m) = s, B(m) = \(\{0^{+(m-1)}\}\), string X(m) = \(\{0\) and Y(m) = \(1^{+(m-1)}\}\).
- Repeat this:
- Subtract k by 1
- Set s(k) = s(k+1)
- Repeat this:
- Subtract s(k) by 1
- If level of A
_{s(k)}< level of A_{s(k+1)}, then break the repeating, or else continue repeating.

- If level of A
_{s(k)}< level of B(k+1), then let string P and Q be such that A_{1}= P A_{s(k)+1}Q, then change the original brace A_{1}into P X(k+1) A_{s(k)+1}Y(k+1) Q, and return. Or else - - If k = 0, then break the repeating, or else -
- Let string X(k) and Y'(k) be such that S
_{s(k)}= X(k) S_{s(k+1)}1 Y'(k), set Y(k) = 1 Y'(k) and set B(k) = X(k) Y'(k).

- Let string P and Q be such that S
_{s(0)}= P S_{s(1)}Q, then apply S_{s(0)}= P P ... P P Q Q ... Q Q with n P's and n Q's, and return.

- Case A4: Otherwise, continue scanning to right.

- Case B: If there's a non-0 number, delete 0's immediately before it until there isn't one, then

- Case B1: If R is immediately before it, then apply \(nRa+1\odot=(\cdots(nRa\odot) Ra\odot\cdots) Ra\odot\) with n \(Ra\odot\)'s. And return.
- Case B2: If lbrace is immediately before it, then apply \(\{a+1\odot\}=\{a\odot\}0\{a\odot\}0\cdots0\{a\odot\}\) with n \(\{a\odot\}\)'s (here n is the base number). And return.
- Case B3: If a separator is immediately before it, then apply \(\{\odot\}a+1=\{\odot\}1\{\odot\}a\), add s by 1 then set A
_{s}= \(\{\odot\}\), then scan on the first \(\{\odot\}\).

- Case C: If there's a brace not separator, add s by 1 then set A
_{s}to that brace, then continue scanning inside it.

The \(\odot\) can be any string or empty.

### Levels

First, we see the whole string after the "R" as an invisible brace here and it has the lowest level (and it cannot appear in other places), 0 has the second lowest level, and others have higher level. We can compare the level of A and B as follows:

- Use subrule on A and B until the subrule cannot apply any more.
- Change all the positive integer k into {0}{0}...{0} with k {0}'s.
- Let \(A=\{A_I^{+a}\}\) and \(B=\{B_I^{+b}\}\)
- If a>b then A>B on level; If a<b then A<B on level. or else -
- All the separators of A are {A
_{1}}, {A_{2}},... {A_{n}}. And the same as B. - Compare levels of {A
_{i}}'s and find highest-level ones - {A_{M}}. And the same as B. - If level of {A
_{M}}>{B_{M}}, then A>B; if {A_{M}}<{B_{M}}, then A<B. or else - - If the amount of {A
_{M}}>{B_{M}}, then A>B; if the amount of {A_{M}}<{B_{M}}, then A<B. or else - - Find the last {A
_{M}} of A, and A={A^{-}{A_{M}}A^{+}} and the same as B. - If the level of {A
^{+}}>{B^{+}}, then A>B; if {A^{+}}<{B^{+}}, then A<B. or else - - If the level of {A
^{-}}>{B^{-}}, then A>B; if {A^{-}}<{B^{-}}, then A<B; if {A^{-}}={B^{-}}, then A=B.

## Explanation

What's new in R function II:

- Remove the ill-definition of enclosers. The cost is, the rules become more complex.
- Using superscript "+m" to present the "brace rank" \(\{A^{+m}\}\). This allow something like \(nR\{0\{0^{+8}\}2\}\), which must be written as many braces as nR{0{0{0{0{0{0{0,,,,,,,2}1}1}1}1}1}1} in the version 1.
- The "brace rank" has an offset. {0
^{+1}} (or the comma, or {0^{+}}) in version 2 is corresponding to the {0,1} in version 1, {0^{+2}} in version 2 is corresponding to the comma in version 1, {0^{+(m+1)}} in version 2 is corresponding to the m-ple comma in version 1. That make LAN in R function II much weaker, but the final strength of the two version are the same. - The {0} doesn't reduce to n, but reduces to 1. So we can use an expression such that numbers over 1 don't appear in the string.
- Change the base rule a little. But this doesn't affect much.

### Up to linear array notation

Basic R function remains almost the same. Just the base rule changes - now It's nR0 = 2^n.

The {0} doesn't reduce to n, but reduces to 1, so the brace notation change a little.

Here I bring something called *standard string*. A standard string doesn't contain numbers over 1, that means, only 0 and 1 appear. For example, 3R2 = 3R1R1R1, and at the same time 3R{0}{0} = 3R1{0} = 3R{0}R{0}R{0} = 3R1R1R1 - they are the same! nR{{2}{3}} and nR{{1{0}}{1{0}{0}}} are the same, too. Notice that a {0} reduces to 1 no matter what the base number n is, so we can change {0} into 1, change 1 into {0} at any time (but we must use {0}'s when compare levels). **So a number k is equivalent to the string {0}{0}...{0} with k {0}'s**.

However, linear array notation changes a lot. For example, 3R{{0,2},2} = 3R{{0{0{01,1}1,1}1,1},2} = 3R{{{{1,1}{0},1}{0},1},2} (exactly) = 3R{{{{1,1},1},1},2} (approximately), while in version 1 3R{{0,2},2}= 3R{{{{{{0,2},1},2},1},2},1}, the latter one is larger.

A more complex example: how to solve 3R{0,{0,0,2},3}{0,0,{1}}. First scanning, when we scan to the comma, the brace become 3R{0,{0,0**,**1,1},3}{0,0,{1}}, and now we meet case A3. Here A_{1} = {0,{0,0,2},3}{0,0,{1}}, A_{2} = {0,{0,0,2},3}, A_{3} = {0,0,2}, A_{4} is comma. Then step 1 and 2: S_{1} = {0,{0,0,1,1},3}{0,0,{1}}, S_{2} = {0,{0,0,1,1},3}, S_{3} = {0,0,1,1}, S_{4} is comma. Then step 3: m = 1, so set k = 1, s(1) = 4, B(1) = {0}, X(1) = "{0", Y(1) = "1}". Then step 4. Step 4.1: set k = 0. Step 4.2: set s(0) = 4. Step 4.3 is the "searching process", we get s(0) = 3 finally. Passing step 4.4, and break the repeating in step 4.5. Step 5: P = "{0,0", Q = "1,1}", then apply {0,0,1,1} -> {0,0{0,0{0,01,1}1,1}1,1} = {0,{0,{0,1,1}{0},1}{0},1}. When we finally return, we get 3R{0,{0,0,2},3}{0,0,{1}} = 3R{0,{0,{0,{0,1,1}{0},1}{0},1},3}{0,0,{1}}.

In LAN, it seems that B(k), X(k), Y(k) and step 4.4 are no use, and we just simply get s(0) = s(1) -1 in step 4.3 of case A3.

And more, we can write a ruleset for LAN as follows. The 5th rule changes and make LAN weaker.

- \(nR0=2^n\)
- \(nRa+1\odot=nRa\odot Ra\odot...Ra\odot\) with n R's.
- \(nR\oslash\{0\}\odot=nR\oslash 1\odot\)
- \(nR\oslash\{a+1\odot_1\}\odot_2=nR\oslash\{a\odot_1\}\{a\odot_1\}...\{a\odot_1\}\odot_2\) with n \(\{a\odot_1\}\)'s.
- \(nR\oslash_2\{\oslash_10,a+1\odot_1\}\odot_2=\) \(nR\oslash_2\{\oslash_1\{\oslash_1...\{\oslash_11,a\odot_1\}...1,a\odot_1\}1,a\odot_1\}\odot_2\) with n \(\{\oslash_1\)'s and n \(1,a\odot_1\}\)'s.
- 0 is default, so 0's immediately before a brace can be removed, and the same to 0's at the end of an array. i.e. 0{={ and ,0}=}