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单词 CategoryOfQuiversIsConcrete
释义

category of quivers is concrete


Let 𝒬 denote the categoryMathworldPlanetmath of all quivers and quiver morphismsMathworldPlanetmath with standard composition. If Q=(Q0,Q1,s,t) is a quiver, then we can associate with Q the set

S(Q)=Q0Q1

where ,,” denotes the disjoint unionMathworldPlanetmathPlanetmath of sets.

Furthermore, if F:QQ is a morphism of quivers, then F induces function

S(F):S(Q)S(Q)

by putting S(F)(a)=F0(a) if aQ0 and S(F)(α)=F1(α) if αQ1.

PropositionPlanetmathPlanetmathPlanetmath. The category 𝒬 together with S:𝒬𝒮𝒯 is a concrete category over the category of all sets 𝒮𝒯.

Proof. The fact that S is a functorMathworldPlanetmath we leave as a simple exercise. Now assume, that F,G:QQ are morphisms of quivers such that S(F)=S(G). It follows, that for any vertex aQ0 and any arrow αQ1 we have

F0(a)=S(F)(a)=S(G)(a)=G0(a);
F1(α)=S(F)(α)=S(G)(α)=G1(α)

which clearly proves that F=G. This completesPlanetmathPlanetmathPlanetmathPlanetmathPlanetmath the proof.

Remark. Note, that if F:QQ is a morphism of quivers, then F is injectivePlanetmathPlanetmath in (𝒬,S) (see this entry (http://planetmath.org/InjectiveAndSurjectiveMorphismsInConcreteCategories) for details) if and only if both F0, F1 are injective. The same holds if we replace word ,,injective” with ,,surjectivePlanetmathPlanetmath”.

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更新时间:2025/5/4 4:46:20