PhyslibAlpha.ProbabilisticTheory.Algebra.Alternative
Alternative algebras
i. Overview
An algebra is alternative when the associator `(a, b, c) = (a b) c - a (b c)` is alternating. The octonions are alternative, and they coordinatize the exceptional Albert Jordan algebra. Alternative algebras satisfy the flexible law and the left Moufang identity.
ii. Key results
- `IsAlternative` : alternative algebras.
- `associator` : the associator.
- `IsAlternative.mul_flexible` : the flexible law.
- `IsAlternative.moufang_left` : the left Moufang identity.
15 declarations
Semigroups are Alternative Algebras
Every semigroup is an alternative algebra. That is, if the multiplication in is associative, then the associator satisfies the alternating property.
Associator
For elements in an algebra , the associator is defined as the ternary operation , which measures the failure of the associative law.
In an alternative algebra , for any elements , the associator satisfies the left-additive identity , where the associator is defined as .
Additivity of the Associator in the Middle Argument
In an algebra , the associator of three elements is defined as . For any elements , the associator is additive in its middle argument:
The associator is additive in its third argument
For any elements , and in an algebra , the associator is additive in its third argument, satisfying the identity .
Teichmüller's Identity for the Associator
For any elements in an algebra , let the associator be defined as . Then the following identity holds: This is known as Teichmüller's identity and holds in any non-associative algebra.
The left alternative identity
In an alternative algebra , for any elements , the associator is equal to .
The associator identity in alternative algebras
In an alternative algebra , for any elements , the associator of is zero, which is expressed as . Using the definition of the associator, this implies the right alternative law .
in Alternative Algebras
In an alternative algebra , for any elements , the associator is skew-symmetric with respect to the first two arguments, satisfying .
In an alternative algebra , for any elements , the associator satisfies the identity .
for the Associator
In an alternative algebra , the associator is cyclically invariant. That is, for any elements , it holds that .
The associator
In an alternative algebra , for any elements , the associator , defined as , is equal to .
Flexible Law:
In an alternative algebra , for any two elements , the flexible law holds.
Left Moufang identity
In an alternative algebra , for any elements , the left Moufang identity holds: where the associator is alternating.
McCrimmon's Left Bumping Formula:
In an alternative algebra , for any , the following identity holds: where denotes the associator. This result is known as McCrimmon's left bumping formula, a key alternative-algebra identity used in the study of Albert matrices.
