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We investigate preserving of projectivity and injectivity by the object-wise tensor product of $R\Bbb{C}$-modules, where $\Bbb{C}$ is a small category. In particular, let ${\cal O}(G,X)$ be the category of canonical orbits of a discrete group $G$, over a $G$-set $X$. We show that projectivity of $R{\cal O}(G,X)$-modules is preserved by this tensor product. Moreover, if $G$ is a finite group, $X$ a finite $G$-set and $R$ is an integral domain then such a tensor product of two injective $R{\cal O}(G,X)$-modules is again injective.
@article{TAC_2000_7_a10, author = {Marek Golasinski}, title = {On the object-wise tensor product of functors to modules}, journal = {Theory and applications of categories}, pages = {226--235}, publisher = {mathdoc}, volume = {7}, year = {2000}, language = {en}, url = {http://geodesic.mathdoc.fr/item/TAC_2000_7_a10/} }
Marek Golasinski. On the object-wise tensor product of functors to modules. Theory and applications of categories, Tome 7 (2000), pp. 226-235. http://geodesic.mathdoc.fr/item/TAC_2000_7_a10/