Example of a commutative non-associative magma
In mathematics, it can be shown that there exist magmas that are commutative but not associative. A simple example of such a magma is given by considering the children's game of rock, paper, scissors.
A commutative non-associative magma
![](../I/m/Integer_examples_for_groups_and_non-groups_svg.svg.png)
Let and consider the binary operation
defined, loosely inspired by the rock-paper-scissors game, as follows:
"paper beats rock";
"scissors beat paper";
"rock beats scissors";
"rock ties with rock";
"paper ties with paper";
"scissors tie with scissors".
The last three equations show the additional property of idempotence of such magma, whose Cayley table results to be:
By definition, the magma is commutative, but it is also non-associative, as the following shows:
but
See the bottom row in the picture for more example operations, defined on the integer numbers.
A commutative non-associative algebra
Using the above example, one can construct a commutative non-associative algebra over a field : take
to be the three-dimensional vector space over
whose elements are written in the form
,
for . Vector addition and scalar multiplication are defined component-wise, and vectors are multiplied using the above rules for multiplying the elements
and
. The set
i.e.
forms a basis for the algebra . As before, vector multiplication in
is commutative, but not associative.