منابع مشابه
Characterising E-projectives via Comonads
This paper demonstrates the usefulness of a comonadic approach to give previously unknown characterisation of projective objects in certain categories over particular subclasses of epimorphisms. This approach is a simple adaptation of a powerful technique due to M. Escardó which has been used extensively to characterise injective spaces and locales over various kinds of embeddings, but never pr...
متن کاملGraded Comodule Categories with Enough Projectives
It is well-known that the category of comodules over a flat Hopf algebroid is abelian but typically fails to have enough projectives, and more generally, the category of graded comodules over a graded flat Hopf algebroid is abelian but typically fails to have enough projectives. In this short paper we prove that the category of connective graded comodules over a connective, graded, flat, finite...
متن کاملAlgebraic Categories Whose Projectives Are Explicitly Free
Let M = (M,m,u) be a monad and let (MX,m) be the free M-algebra on the object X. Consider an M-algebra (A, a), a retraction r : (MX,m) → (A, a) and a section t : (A, a) → (MX,m) of r. The retract (A, a) is not free in general. We observe that for many monads with a ‘combinatorial flavor’ such a retract is not only a free algebra (MA0,m), but it is also the case that the object A0 of generators ...
متن کاملAsymptotiques de nombres de Betti d’hypersurfaces projectives réelles
On s’intéresse à la valeur maximale des nombres de Betti bi(RX n m) pour i,m, n fixés où RX n m est la partie réelle d’une hypersurface réelle X m non singulière de degré m dans l’espace projectif complexe CP, ainsi qu’à la valeur maximale des nombres de Betti bi(RY n 2k) pour i, k, n fixés où RY n 2k est la partie réelle d’un revêtement double réel de CP ramifié sur une hypersurface réelle non...
متن کاملOn Satellites in Semi-abelian Categories: Homology without Projectives
Working in a semi-abelian context, we use Janelidze’s theory of generalised satellites to study universal properties of the Everaert long exact homology sequence. This results in a new definition of homology which does not depend on the existence of projective objects. We explore the relations with other notions of homology, and thus prove a version of the higher Hopf formulae. We also work out...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
ژورنال
عنوان ژورنال: Nagoya Mathematical Journal
سال: 1966
ISSN: 0027-7630,2152-6842
DOI: 10.1017/s0027763000026520