BULLETIN OF THE IRANIAN MATHEMATICAL SOCIETY, vol.45, no.2, pp.429-445, 2019 (SCI-Expanded)
In this paper, we study retractable modules and coretractable modules over a formal triangular matrix ring T = [A O M B], where A and B are rings and M is a (B,A)-bimodule. We determine necessary and sufficient conditions for a T-module to be, respectively, retractable or coretractable. We also characterize the right Kasch formal triangular matrix rings. Some examples are provided to illustrate and delimit our results.