Interchange Rings
  An interchange ring,(R,+,*)is an abelian group with a second binary operation defined so that the interchange law (x+y)*(u+v)=(x*u)+(y*v)holds. An interchange near ring is the same structure based on a group which may not be abelian. It is shown that given any group,G,each interchange(near)ring based on that group is formed from a pair of endomorphisms of G whose images commute, and that all interchange (near)rings based on G can be characterized in this manner. To obtain an associative interchange ring, the endomorphisms must be commuting idempotents in the endomorphism semigroup of G. When G is abelian we develop a group theoretic analogue of the simultaneous diagonalization of idempotent linear operators and show that pairs of endomorphisms which yield associative interchange rings can be diagonalized and then put into a canonical form. A best possible upper bound of 4^r can be given for the number of distinct isomorphism classes of associative interchange rings based on a finite abelian group A which is a direct sum of r cyclic groups of prime power order. If A is direct sum of r copies of the same cyclic group of prime power order, we show that there are exactly (r+1)(r+2)(r+3)/6 distinct isomorphism classes of associative interchange rings based on A. Several examples are given and further comments are made about the general theory of interchange rings. 
Charles Edmunds
math.RA