Bourbaki

Exercise 4, § 6

Tag 03J2, permanent. Cite it as [Bourbaki, Tag 03J2].

Theory of Sets, II, 127

Let G be the graph of an equivalence on a set E. Show that if A is a graph such that A⊂G\mathrm{A} \subset \mathrm{G} and pr1A=E\mathrm{pr_1A} = \mathrm{E} (resp. pr2A=E\mathrm{pr_2A} = \mathrm{E}), then

G∘A=G(resp.A∘G=G);\mathrm{G} \circ \mathrm{A} = \mathrm{G} \quad (\text{resp.} \quad \mathrm{A} \circ \mathrm{G} = \mathrm{G});

furthermore, if BB is any graph, we have (G∩B)∘A=G∩(B∘A)(G \cap B) \circ A = G \cap (B \circ A) (resp. A∘(G∩B)=G∩(A∘B)A \circ (G \cap B) = G \cap (A \circ B)).

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Transcribed from the printed volume. Not translated.