We describe decompositions of the group of units of a ring and of its subgroups, induced by idempotents with certain properties. The results apply to several classes of rings, most notably to semiperfect rings.

Much recent research has focused on the applications of games with ω-regular objectives in the control and verification of reactive systems. However, many of the game-based models are ill-suited for these applications, because they assume that each player has complete information about the state of the system (they are “perfect-information” games). This is because in many situations, a controll...

Let M be a left module over a ring R and I an ideal of R. We call (P,f ) a projective I -cover of M if f is an epimorphism from P to M , P is projective, Kerf ⊆ IP , and whenever P = Kerf + X, then there exists a summand Y of P in Kerf such that P = Y +X. This definition generalizes projective covers and projective δ-covers. Similar to semiregular and semiperfect rings, we characterize I -semir...