Alternativity
In abstract algebra, alternativity is a property of a binary operation. A magma is said to be ' if for all and ' if for all. A magma that is both left and right alternative is said to be .
Any associative magma is alternative. More generally, a magma in which every pair of elements generates an associative submagma must be alternative. The converse, however, is not true, in contrast to the situation in alternative algebras.
Examples
Examples of algebraic structures with an alternative multiplication include:- Any semigroup is associative and therefore alternative.
- Moufang loops are alternative and flexible but generally not associative. See for more examples.
- Octonion multiplication is alternative and flexible. The same is more generally true for any octonion algebra.
- Applying the Cayley-Dickson construction once to a commutative ring with a trivial involution gives a commutative associative algebra. Applying it twice gives an associative algebra. Applying it three times gives an alternative algebra. Applying it four or more times gives an algebra that is typically not alternative. An example is the sequence where is the algebra of quaternions, is the algebra of octonions, and is the algebras of sedenions.