Definition 23: A ring r is a commutative ring if ab= ba for all a, bER. A ring r is an unitary ring if there is lER such that la= al a for all aeR. Such an element is called a multiplicative identity.◆Definition 23: A ring R is a commutative ring if ab = ba for all a, bR . A ring R is an unitary ring if there is 1R such that 1a = a1 = a for all aR. Such an element is called a multiplicative identity