Ring-like structures with two binary operations and no other restrictions are a broad class, one which is too general to study. For this reason, the best-known kinds of non-associative algebras satisfy identities, or properties, which simplify multiplication somewhat. These include the following ones.
Let x, y and z denote arbitrary elements of the algebra A over the field K. Let powers to positive (non-zero) integer be recursively defined by x1 ≝ x and either xn+1 ≝ xnx3 (right powers) or xn+1 ≝ xxn45 (left powers) depending on authors.
For K of any characteristic:
If K ≠ GF(2) or dim(A) ≤ 3:
If char(K) ≠ 2:
If char(K) ≠ 3:
If char(K) ∉ {2,3,5}:
If char(K) = 0:
If char(K) = 2:
Main article: Associator
The associator on A is the K-multilinear map [ ⋅ , ⋅ , ⋅ ] : A × A × A → A {\displaystyle [\cdot ,\cdot ,\cdot ]:A\times A\times A\to A} given by
It measures the degree of nonassociativity of A {\displaystyle A} , and can be used to conveniently express some possible identities satisfied by A.
Let x, y and z denote arbitrary elements of the algebra.
The nucleus is the set of elements that associate with all others:36 that is, the n in A such that
The nucleus is an associative subring of A.
The center of A is the set of elements that commute and associate with everything in A, that is the intersection of
with the nucleus. It turns out that for elements of C(A) it is enough that two of the sets ( [ n , A , A ] , [ A , n , A ] , [ A , A , n ] ) {\displaystyle ([n,A,A],[A,n,A],[A,A,n])} are { 0 } {\displaystyle \{0\}} for the third to also be the zero set.
More classes of algebras:
See also: list of algebras
There are several properties that may be familiar from ring theory, or from associative algebras, which are not always true for non-associative algebras. Unlike the associative case, elements with a (two-sided) multiplicative inverse might also be a zero divisor. For example, all non-zero elements of the sedenions have a two-sided inverse, but some of them are also zero divisors.
The free non-associative algebra on a set X over a field K is defined as the algebra with basis consisting of all non-associative monomials, finite formal products of elements of X retaining parentheses. The product of monomials u, v is just (u)(v). The algebra is unital if one takes the empty product as a monomial.38
Kurosh proved that every subalgebra of a free non-associative algebra is free.39
An algebra A over a field K is in particular a K-vector space and so one can consider the associative algebra EndK(A) of K-linear vector space endomorphism of A. We can associate to the algebra structure on A two subalgebras of EndK(A), the derivation algebra and the (associative) enveloping algebra.
Main article: Derivation algebra
A derivation on A is a map D with the property
The derivations on A form a subspace DerK(A) in EndK(A). The commutator of two derivations is again a derivation, so that the Lie bracket gives DerK(A) a structure of Lie algebra.40
There are linear maps L and R attached to each element a of an algebra A:41
Here each element L ( a ) , R ( a ) {\displaystyle L(a),R(a)} is regarded as an element of EndK(A). The associative enveloping algebra or multiplication algebra of A is the sub-associative algebra of EndK(A) generated by the left and right linear maps L ( a ) , R ( a ) {\displaystyle L(a),R(a)} .4243 The centroid of A is the centraliser of the enveloping algebra in the endomorphism algebra EndK(A). An algebra is central if its centroid consists of the K-scalar multiples of the identity.44
Some of the possible identities satisfied by non-associative algebras may be conveniently expressed in terms of the linear maps:45
The quadratic representation Q is defined by46
or equivalently,
The article on universal enveloping algebras describes the canonical construction of enveloping algebras, as well as the PBW-type theorems for them. For Lie algebras, such enveloping algebras have a universal property, which does not hold, in general, for non-associative algebras. The best-known example is, perhaps the Albert algebra, an exceptional Jordan algebra that is not enveloped by the canonical construction of the enveloping algebra for Jordan algebras.
Schafer 1995, Chapter 1. - Schafer, Richard D. (1995) [1966]. An Introduction to Nonassociative Algebras. Dover. ISBN 0-486-68813-5. Zbl 0145.25601. https://books.google.com/books?isbn=0486688135 ↩
Schafer 1995, p. 1. - Schafer, Richard D. (1995) [1966]. An Introduction to Nonassociative Algebras. Dover. ISBN 0-486-68813-5. Zbl 0145.25601. https://books.google.com/books?isbn=0486688135 ↩
Albert 1948a, p. 553. - Albert, A. Adrian (1948a). "Power-associative rings". Transactions of the American Mathematical Society. 64: 552–593. doi:10.2307/1990399. ISSN 0002-9947. JSTOR 1990399. MR 0027750. Zbl 0033.15402. https://doi.org/10.2307%2F1990399 ↩
Schafer 1995, p. 30. - Schafer, Richard D. (1995) [1966]. An Introduction to Nonassociative Algebras. Dover. ISBN 0-486-68813-5. Zbl 0145.25601. https://books.google.com/books?isbn=0486688135 ↩
Schafer 1995, p. 128. - Schafer, Richard D. (1995) [1966]. An Introduction to Nonassociative Algebras. Dover. ISBN 0-486-68813-5. Zbl 0145.25601. https://books.google.com/books?isbn=0486688135 ↩
Schafer 1995, p. 3. - Schafer, Richard D. (1995) [1966]. An Introduction to Nonassociative Algebras. Dover. ISBN 0-486-68813-5. Zbl 0145.25601. https://books.google.com/books?isbn=0486688135 ↩
Okubo 2005, p. 12. - Okubo, Susumu (2005) [1995]. Introduction to Octonion and Other Non-Associative Algebras in Physics. Montroll Memorial Lecture Series in Mathematical Physics. Vol. 2. Cambridge University Press. doi:10.1017/CBO9780511524479. ISBN 0-521-01792-0. Zbl 0841.17001. https://books.google.com/books?isbn=0521017920 ↩
Schafer 1995, p. 91. - Schafer, Richard D. (1995) [1966]. An Introduction to Nonassociative Algebras. Dover. ISBN 0-486-68813-5. Zbl 0145.25601. https://books.google.com/books?isbn=0486688135 ↩
Okubo 2005, p. 13. - Okubo, Susumu (2005) [1995]. Introduction to Octonion and Other Non-Associative Algebras in Physics. Montroll Memorial Lecture Series in Mathematical Physics. Vol. 2. Cambridge University Press. doi:10.1017/CBO9780511524479. ISBN 0-521-01792-0. Zbl 0841.17001. https://books.google.com/books?isbn=0521017920 ↩
Schafer 1995, p. 5. - Schafer, Richard D. (1995) [1966]. An Introduction to Nonassociative Algebras. Dover. ISBN 0-486-68813-5. Zbl 0145.25601. https://books.google.com/books?isbn=0486688135 ↩
Okubo 2005, p. 18. - Okubo, Susumu (2005) [1995]. Introduction to Octonion and Other Non-Associative Algebras in Physics. Montroll Memorial Lecture Series in Mathematical Physics. Vol. 2. Cambridge University Press. doi:10.1017/CBO9780511524479. ISBN 0-521-01792-0. Zbl 0841.17001. https://books.google.com/books?isbn=0521017920 ↩
McCrimmon 2004, p. 153. - McCrimmon, Kevin (2004). A taste of Jordan algebras. Universitext. Berlin, New York: Springer-Verlag. doi:10.1007/b97489. ISBN 978-0-387-95447-9. MR 2014924. Zbl 1044.17001. Errata. https://books.google.com/books?isbn=9780387954479 ↩
Schafer 1995, p. 28. - Schafer, Richard D. (1995) [1966]. An Introduction to Nonassociative Algebras. Dover. ISBN 0-486-68813-5. Zbl 0145.25601. https://books.google.com/books?isbn=0486688135 ↩
Okubo 2005, p. 16. - Okubo, Susumu (2005) [1995]. Introduction to Octonion and Other Non-Associative Algebras in Physics. Montroll Memorial Lecture Series in Mathematical Physics. Vol. 2. Cambridge University Press. doi:10.1017/CBO9780511524479. ISBN 0-521-01792-0. Zbl 0841.17001. https://books.google.com/books?isbn=0521017920 ↩
Okubo 2005, p. 17. - Okubo, Susumu (2005) [1995]. Introduction to Octonion and Other Non-Associative Algebras in Physics. Montroll Memorial Lecture Series in Mathematical Physics. Vol. 2. Cambridge University Press. doi:10.1017/CBO9780511524479. ISBN 0-521-01792-0. Zbl 0841.17001. https://books.google.com/books?isbn=0521017920 ↩
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It follows from the Artin's theorem. /wiki/Artin%27s_theorem ↩
Jacobson 1968, p. 36. - Jacobson, Nathan (1968). Structure and representations of Jordan algebras. American Mathematical Society Colloquium Publications, Vol. XXXIX. Providence, R.I.: American Mathematical Society. ISBN 978-0-821-84640-7. MR 0251099. https://books.google.com/books?isbn=9780821846407 ↩
Schafer 1995, p. 92. - Schafer, Richard D. (1995) [1966]. An Introduction to Nonassociative Algebras. Dover. ISBN 0-486-68813-5. Zbl 0145.25601. https://books.google.com/books?isbn=0486688135 ↩
Kokoris 1955, p. 710. - Kokoris, Louis A. (1955). "Power-associative rings of characteristic two". Proceedings of the American Mathematical Society. 6 (5). American Mathematical Society: 705–710. doi:10.2307/2032920. https://doi.org/10.2307%2F2032920 ↩
Albert 1948b, p. 319. - Albert, A. Adrian (1948b). "On right alternative algebras". Annals of Mathematics. 50: 318–328. doi:10.2307/1969457. JSTOR 1969457. https://doi.org/10.2307%2F1969457 ↩
Mikheev 1976, p. 179. - Mikheev, I.M. (1976). "Right nilpotency in right alternative rings". Siberian Mathematical Journal. 17 (1): 178–180. doi:10.1007/BF00969304. https://doi.org/10.1007%2FBF00969304 ↩
Zhevlakov et al. 1982, p. 343. - Zhevlakov, Konstantin A.; Slin'ko, Arkadii M.; Shestakov, Ivan P.; Shirshov, Anatoly I. (1982) [1978]. Rings that are nearly associative. Translated by Smith, Harry F. ISBN 0-12-779850-1. https://www.researchgate.net/publication/260600596_Rings_that_are_nearly_associative ↩
Schafer 1995, p. 148. - Schafer, Richard D. (1995) [1966]. An Introduction to Nonassociative Algebras. Dover. ISBN 0-486-68813-5. Zbl 0145.25601. https://books.google.com/books?isbn=0486688135 ↩
Bremner, Murakami & Shestakov 2013, p. 18. - Bremner, Murray; Murakami, Lúcia; Shestakov, Ivan (2013) [2006]. "Chapter 86: Nonassociative Algebras" (PDF). In Hogben, Leslie (ed.). Handbook of Linear Algebra (2nd ed.). CRC Press. ISBN 978-1-498-78560-0. https://www.math.uci.edu/~brusso/BremnerEtAl35pp.pdf ↩
Bremner, Murakami & Shestakov 2013, pp. 18–19, fact 6. - Bremner, Murray; Murakami, Lúcia; Shestakov, Ivan (2013) [2006]. "Chapter 86: Nonassociative Algebras" (PDF). In Hogben, Leslie (ed.). Handbook of Linear Algebra (2nd ed.). CRC Press. ISBN 978-1-498-78560-0. https://www.math.uci.edu/~brusso/BremnerEtAl35pp.pdf ↩
Albert 1948a, p. 554, lemma 4. - Albert, A. Adrian (1948a). "Power-associative rings". Transactions of the American Mathematical Society. 64: 552–593. doi:10.2307/1990399. ISSN 0002-9947. JSTOR 1990399. MR 0027750. Zbl 0033.15402. https://doi.org/10.2307%2F1990399 ↩
Albert 1948a, p. 554, lemma 3. - Albert, A. Adrian (1948a). "Power-associative rings". Transactions of the American Mathematical Society. 64: 552–593. doi:10.2307/1990399. ISSN 0002-9947. JSTOR 1990399. MR 0027750. Zbl 0033.15402. https://doi.org/10.2307%2F1990399 ↩
Schafer 1995, p. 14. - Schafer, Richard D. (1995) [1966]. An Introduction to Nonassociative Algebras. Dover. ISBN 0-486-68813-5. Zbl 0145.25601. https://books.google.com/books?isbn=0486688135 ↩
McCrimmon 2004, p. 56. - McCrimmon, Kevin (2004). A taste of Jordan algebras. Universitext. Berlin, New York: Springer-Verlag. doi:10.1007/b97489. ISBN 978-0-387-95447-9. MR 2014924. Zbl 1044.17001. Errata. https://books.google.com/books?isbn=9780387954479 ↩
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Schafer 1995, p. 4. - Schafer, Richard D. (1995) [1966]. An Introduction to Nonassociative Algebras. Dover. ISBN 0-486-68813-5. Zbl 0145.25601. https://books.google.com/books?isbn=0486688135 ↩
Okubo 2005, p. 24. - Okubo, Susumu (2005) [1995]. Introduction to Octonion and Other Non-Associative Algebras in Physics. Montroll Memorial Lecture Series in Mathematical Physics. Vol. 2. Cambridge University Press. doi:10.1017/CBO9780511524479. ISBN 0-521-01792-0. Zbl 0841.17001. https://books.google.com/books?isbn=0521017920 ↩
Albert 2003, p. 113. - Albert, A. Adrian (2003) [1939]. Structure of algebras. American Mathematical Society Colloquium Publ. Vol. 24 (Corrected reprint of the revised 1961 ed.). New York: American Mathematical Society. ISBN 0-8218-1024-3. Zbl 0023.19901. https://books.google.com/books?isbn=0821810243 ↩
McCrimmon 2004, p. 57. - McCrimmon, Kevin (2004). A taste of Jordan algebras. Universitext. Berlin, New York: Springer-Verlag. doi:10.1007/b97489. ISBN 978-0-387-95447-9. MR 2014924. Zbl 1044.17001. Errata. https://books.google.com/books?isbn=9780387954479 ↩
Koecher 1999, p. 57. - Koecher, Max (1999). Krieg, Aloys; Walcher, Sebastian (eds.). The Minnesota notes on Jordan algebras and their applications. Lecture Notes in Mathematics. Vol. 1710. Berlin: Springer-Verlag. ISBN 3-540-66360-6. Zbl 1072.17513. https://books.google.com/books?isbn=3540663606 ↩