COLLOQUIUM MATHEMATICUM, cilt.127, sa.1, ss.67-81, 2012 (SCI-Expanded)
We investigate when the direct sum of semi-projective modules is semi-projective. It is proved that if R is a right Ore domain with right quotient division ring Q not equal R and X is a free right R-module then the right R-module Q circle plus X is semi-projective if and only if there does not exist an R-epimorphism from X to Q