Cartan–Brauer–Hua theorem
In abstract algebra, the Cartan-Brauer-Hua theorem is a theorem pertaining to division rings. It says that given two division rings such that xKx−1 is contained in K for every x not equal to 0 in D, either K is contained in the center of D, or. In other words, if the unit group of K is a normal subgroup of the unit group of D, then either or K is central.
