We study homological algebra in the abelian categoryΓ, whose objects are functors from finite pointed sets to vector spaces over F p . The full calculation of T orΓ * -groups between functors of degree not exceeding p is presented. We compare our calculations with known results on homology of symmetric groups, Steenrod algebra and functor homology computations in the abelian category F of functors from vector spaces over F p to itself.
Introduction.In recent years we observe growing interest in homological algebra computations in various categories of functors from small categories to vector spaces. Let Γ be the category of finite pointed sets. By Γ-module we understand a functor from Γ to vector spaces over a finite field F p . The following paper is the first in a series devoted to studying homological algebra in the category of Γ-modules, which will be denoted byΓ. The homological algebra in the categoryΓ is of crucial importance because of its close relations to Steenrod algebra and algebraic topology in general. The subject is well documented in the literature, see for example [BS]If we denote by V p the category of finite dimensional vector spaces over F p and by F the category of functors from V p to V ect F p then one can say that homological algebra in F is well understood because of calculations and methods developed during the last ten years with a culmination in [FFSS]. But some questions still remain open. Let L ∈Γ be a linearization functor which takes a pointed set X with a distinguished point 0 to. CategoriesΓ and F are related by the functor l : F →Γ via the formula l(T ) = T • L and hence their homological algebras are also related. This correspondence was preliminary studied in [B2] where it was shown how to applyΓ-calculations to obtain new interesting results in F. It seems to us that homological algebra inΓ should be easier than in F and the full knowledge on both should come from their interaction coming from the functor l.We will use the following convention: we will denote by the same letter a functor from F and its precomposition with L. This should not cause any problem in the present paper because the category F will not be used here in any systematic way. If we want to get from T ∈ F a contravariant functor Γ → V ect F p we will precompose it with L * where * denotes the ordinary vector space dualization. In such notation we can say that our ultimate goal is to get full understanding of the T orΓ and ExtΓ groups between functors of exterior (Λ i ), symmetric (S i ) and divided powers (D i ), parallelly to the results of [FFSS]. Notice that * Partially supported by the KBN grant 1P03A 005 26 1