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# nanma80/octonion

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# Octonion

This repo contains a proof-of-concept puzzle on integral octonions, and some scripts to explore octonions. This is a joint work with Roice Nelson. This puzzle is a proof of concept of non-associative puzzles. It was created so that we can have a taste of the difficulty level and non-associative solving experience. We are working on improving it and making it more intuitive. We are also working on other non-associative puzzles. An introduction can be found here.

## How to run the integral octonions puzzle?

• Install Python, 2.* or 3.*.
• Install numpy.
• Run puzzle_python2.py or puzzle_python3.py depending on the Python version you installed.
• Follow the instructions to solve it. You may want to refer to the explanations below.

• Octonions are a number system extended from complex numbers and quaternions.
• Each octonion can be thought of as a vector of 8 real numbers, or a sum of 8 basis vectors.
• Addition, subtraction, multiplication, inverse, norm, conjugate can be defined similar to complex numbers, with a more complicated multiplication table.
• Octonion multiplication is not commutative (a * b != b * a) and not associative ((a * b) * c != a * (b * c)) in general.

• They are octonions whose coordinates are all integers or all half-integers satisfying certain properties.

• The minimum nonzero norm of integral octonions is 1. There are 240 integral octonions with norm = 1.

• The identity octonion, (1, 0, 0, 0, 0, 0, 0, 0), is a unit norm integral octonion.

• The set of 240 unit norm integral octonions is closed under octonion multiplication. That is, the product of two numbers in this set stays in the set.

• If we start from three generators

• i = (0, 1, 0, 0, 0, 0, 0, 0),
• j = (0, 0, 1, 0, 0, 0, 0, 0),
• h = (0, 1, 1, 1, 1, 0, 0, 0)/2,

and use the octonion multiplication *, we can generate all 240 integral octonions with unit norm.

## Summary of the Rubik's Cube, as an analogy:

• All the states of the Rubik's Cube are generated from generators U, D, L, R, F, B, and the group operation of concatenating moves.
• We draw a random one from all the states as the initial state or scramble.
• In each step
• We input any generator individually, or in general, any sequence of generators as an expression.
• (The new state) = (the old state) * (input).
• We win when the state is the identity or "solved" state.

• All the 240 unit norm integral octonions are generated by i, j, and h.
• We pick a random unit norm integral octonion as the initial state or scramble.
• In each step
• We input an expression of i, j, h, and the octonion multiplication *, with parenthesis (). For example, h * (i * j).
• The input expression is evaluated. By construction, it is also a unit norm integral octonion.
• (The new state) = (the old state) * (input expression).
• We win when the state is the identity octonion (1, 0, 0, 0, 0, 0, 0, 0).

## Why input expression rather than individual generators? Non-associativity:

• Since the multiplication is not associative: state * (a * b) != (state * a) * b, applying the expression (a * b) as input is different from applying a and then applying b.
• If you only input i or j or h individually and do not use multiplication in the input expression, it is unlikely (with 20% chance) you will be able to solve the puzzle.
• Therefore, we highly recommend trying at least (i * h) if you are stuck.

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