Elementary divisor domains were defined by Kaplansky [I. Kaplansky, Elementary divisors and modules, Trans. Amer. Math. Soc. 66 (1949) 464–491] and generalized to rings with zero-divisors by Gillman and Henriksen [L. Gillman, M. Henriksen, Some remarks about elementary divisor rings, Trans. Amer. Math. Soc. 82 (1956) 362–365]. In [M.D. Larsen, W.J. Lewis, T.S. Shores, Elementary divisor rings a...

To my wife Kelly. ii ACKNOWLEDGEMENTS I would like to thank, first and foremost, my advisor Harm Derksen for guiding me along the path to becoming a mathematical researcher. The many hours we spent in discussion and his creative suggestions were absolutely essential for completion of this project. I would also like to thank John Stembridge for reading this dissertation and for some helpful disc...

We obtain a description of quasi-endomorphism rings torsion-free Abelian groups G rank 4, quasi-decomposable into direct sum A1 and A2 1 strongly indecomposable group B 2 in the case where quasi-homomorphism ℚ ⨂ Hom(A2,B) has 2.