Communications in Algebra
Let M and N be differential graded (DG) modules over a positively graded commutative DG algebra A. We show that the Ext-groups ExtiA(M,N) defined in terms of semi-projective resolutions are not in general isomorphic to the Yoneda Ext-groups YExtiA(M,N) given in terms of equivalence classes of extensions. On the other hand, we show that these groups are isomorphic when the first DG module is semi-projective.
Nasseh, Saeed, Sean Sather-Wagstaff.
"Extension Groups for DG Modules."
Communications in Algebra, 45 (10): 4466-4476.
doi: 10.1080/00927872.2016.1270292 source: https://doi.org/10.1080/00927872.2016.1270292