Example of a Ring with an Improper Involution
This Demonstration shows an example of an improper involution , that is, does not imply . Let be a commutative ring different from . If is the ring of all 2×2 matrices over , then the involution[more]
is improper. Specifically, for , if , then , even if .[less]
A *-ring (or involutive ring, or ring with involution) is a ring with an involution :
The example based on matrix inversion is taken from [1, p. 11]. For definitions, see [1, p. 3, p. 10].
 S. K. Berberian, Baer *-Rings, New York: Springer-Verlag, 1972.