If A and B are Abelian groups, then Hom(A,B) is also an Abelian group under pointwise addition of functions. In this section we will see how Hom gives rise to classes of functors. Let A denote the category of Abelian groups. A covariant functor T : A → A associates to every Abelian group A an Abelian group T (A), and for every homomorphism f : A → B a homomorphism T (f) : T (A)→ T (B), such tha...

Let R be a commutative Noetherian ring and let M be a nitely generated R-module. If I is an ideal of R generated by M-regular sequence, then we study the vanishing of the rst Tor functors. Moreover, for Artinian modules and coregular sequences we examine the vanishing of the rst Ext functors.

1 Belian categories 2 1.1 Complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Pull-backs and push-outs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3 Ascent functors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.4 Snake Lemma . . . . . . . . . . . . . . . . . . . . . ....

We study the homological algebra in category Pp of strict polynomial functors degree p over a field positive characteristic p. determine decomposition matrix our and we calculate Ext-groups between important from point view representation theory. Our results include computations Ext-algebras simple Schur functors. observe that has Kazhdan-Lusztig theory show DG algebras computing for are formal...

In this paper we compute some derived functors Ext of the internal homomorphism functor in the category of modules over the representation Green functor. This internal homomorphism functor is the left adjoint of the box product. When the group is a cyclic 2-group, we construct a projective resolution of the module fixed point functor, and that allows a direct computation of the graded Green fun...

Artin glueings of frames correspond to adjoint split extensions in the category and finite-meet-preserving maps. We extend these ideas setting toposes show that a 2-categorical notion 2-category toposes, finite-limit-preserving functors natural transformations. A morphism between is introduced, which allows Ext(H,N) be constructed. contravariantly equivalent Hom(H,N), moreover, this can extende...

Let $(R,underline{m})$ be a commutative Noetherian local ring and $M$ be a non-zero finitely generated $R$-module. We show that if $R$ is almost Cohen-Macaulay and $M$ is perfect with finite projective dimension, then $M$ is an almost Cohen-Macaulay module. Also, we give some necessary and sufficient condition on $M$ to be an almost Cohen-Macaulay module, by using $Ext$ functors.

We construct hyper-homology spectral sequences of Z-graded and RO(G)-graded Mackey functors for Ext and Tor over G-equivariant S-algebras (A∞ ring spectra) for finite groups G. These specialize to universal coefficient and Künneth spectral sequences.

Abstract We study a Serre functor in categories related to the category $\mathcal {P}_{d}$ P d of strict polynomial functors over field positive characteristic. Our main result shows that derived affine some cases carries structure Calabi–Yau cate...

Motivated in part by the study of the stable homology of automorphism groups of free groups, we consider cohomological calculations in the category F(gr) of functors from finitely generated free groups to abelian groups. In particular, we compute the groups Ext F(gr) (T ◦a, T◦a) where a is the abelianization functor and T is the n-th tensor power functor for abelian groups. These groups are sho...