[A1] U. Albrecht: 
Endomorphism rings and $A$-projective torsion-free abelian groups. Abelian group theory proceedings, LNM 1006, Springer-Verlag, 1982–3. 
MR 0722620 
[A] D. M. Arnold: 
Finite rank torsion free abelian groups and rings, LNM 931. Springer-Verlag, 1982. 
MR 0665251 
[AP] D. M. Arnold, R. S. Pierce, J.D. Reid, C. Vinsonhaler, W. Wickless: 
Torsion-free abelian groups of finite rank projective as modules over their endomorphism rings. Journal of Algebra 71(1) (1981), 1–10. 
DOI 10.1016/0021-8693(81)90102-2 | 
MR 0627421 
[G] K. R. Goodearl: 
Ring theory: Nonsingular rings and modules. Marcel Dekker, Inc., New York and Basel, 1976. 
MR 0429962 | 
Zbl 0336.16001 
[Go] H. P. Goeters: Flatness and the ring of quasi-endomorphism. submitted.
[R] J. D. Reid: 
On quasi-decompositions of torsion-free abelian groups. Proc. Amer. Math. Soc. 13 (1962), 550–554. 
MR 0137760 | 
Zbl 0113.25401 
[V] C. Vinsonhaler: 
The divisible and $E$-injective hulls of a torsion-free group. Abelian groups and modules. Proceedings of the Udine conference, CISM No. 287, Springer-Verlag, 1984. 
MR 0789815 | 
Zbl 0559.20038 
[VW] C. Vinsonhaler, W. Wickless: 
Injective hulls of torsion-free abelian groups as modules over their endomorphism rings. Mateřídouška 58(1) (1979), 64–69. 
MR 0535843