Structure

coquotients of cocongruences

A cocongruence (or internal equivalence corelation) on an object XX of a category is a parallel pair j1,j2:X⇉Cj_1, j_2 : X \rightrightarrows C which is jointly epimorphic, and such that for every object TT, the image of (−∘j1,−∘j2):Hom⁡(C,T)→Hom⁡(X,T)2({-} \circ j_1, {-} \circ j_2) : \Hom(C, T) \to \Hom(X, T)^2 is an equivalence relation. If pushouts exist (or at least the pushout displayed below), the latter condition is equivalent to the existence of morphisms r:C→X(coreflexivity)s:C→C(cosymmetry)t:C→C⊔j2,X,j1C(cotransitivity)\begin{align*} r & : C \to X & \quad \text{(coreflexivity)} \\ s & : C \to C & \quad \text{(cosymmetry)} \\ t & : C \to C \sqcup_{j_2,X,j_1} C & \quad \text{(cotransitivity)} \end{align*} satisfying the following equations: r∘j1=idXr∘j2=idXs∘j1=j2s∘j2=j1t∘j1=ι1∘j1t∘j2=ι2∘j2\begin{align*} r \circ j_1 & = \id_X & r \circ j_2 & = \id_X \\ s \circ j_1 & = j_2 & s \circ j_2 & = j_1 \\ t \circ j_1 & = \iota_1 \circ j_1 & t \circ j_2 & = \iota_2 \circ j_2 \end{align*} In particular, j1,j2j_1,j_2 is a coreflexive pair. A coquotient of j1,j2j_1,j_2 is an equalizer of j1,j2j_1,j_2. We say that a category has coquotients of cocongruences if every cocongruence has a coquotient. Note that in the case of a category with binary copowers, the corresponding quotient objects X+X↠CX + X \twoheadrightarrow C are also commonly referred to as cocongruences, or as internal equivalence corelations.

Relevant implications

Examples

There are 134 categories with this property.

Counterexamples

There are 5 categories without this property.

Unknown

There are 0 categories for which the database has no information on whether they satisfy this property.

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