T-ideal
Let be a commutative ring and be a free algebra over on a set of non-commuting variables. A two-sided ideal
of is called a -ideal if for any -endomorphism
of .
For example, let be a -algebra. Define to be the set of all polynomial identities (http://planetmath.org/PolynomialIdentityAlgebra) for . Then is a -ideal of . is called the -ideal of of A.