Beck–Chevalley condition and Goursat categories
نویسندگان
چکیده
منابع مشابه
A New Characterisation of Goursat Categories
We present a new characterisation of Goursat categories in terms of special kind of pushouts, that we call Goursat pushouts. This allows one to prove that, for a regular category, the Goursat property is actually equivalent to the validity of the denormalised 3-by-3 Lemma. Goursat pushouts are also useful to clarify, from a categorical perspective, the existence of the quaternary operations cha...
متن کاملOn closure operators, reflections and protolocalisations in Goursat categories
By defining a closure operator on effective equivalence relations in a regular category C, it is possible to establish a bijective correspondence between these closure operators and the regular epireflective subcategories of C, on the model of the closure operators on kernels in homological categories [5]. When C is an exact Goursat category [6], this correspondence restricts to a bijection bet...
متن کاملDescent for Regular Epimorphisms in Barr Exact Goursat Categories
We show that the category of regular epimorphisms in a Barr exact Goursat category is almost Barr exact in the sense that (it is a regular category and) every regular epimorphism in it is an effective descent morphism.
متن کاملGeometric Approach to Goursat Flags
A Goursat flag is a chain Ds ⊂ Ds−1 ⊂ D1 ⊂ D0 = TM of subbundles of the tangent bundle TM such that corank Di = i and Di−1 is generated by the vector fields in Di and their Lie brackets. Engel, Goursat, and Cartan studied these flags and established a normal form for them, valid at generic points of M . Recently Kumpera, Ruiz and Mormul discovered that Goursat flags can have singularities, and ...
متن کاملOn the "Smith is Huq" Condition in S-Protomodular Categories
We study the so-called “Smith is Huq” condition in the context of Sprotomodular categories: two S-equivalence relations centralise each other if and only if their normalisations commute. We prove that this condition is satisfied by every category of monoids with operations equipped with the class S of Schreier split epimorphisms. Some consequences in terms of characterisation of internal struct...
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: Journal of Pure and Applied Algebra
سال: 2017
ISSN: 0022-4049
DOI: 10.1016/j.jpaa.2016.12.031