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In geometry, $\cong$ means congruence of figures, which means the figures have the same shape and size. (In advanced geometry, it means one is the image of the other under a mapping known as an "isometry", which provi...
In mathematical notation, what are the usage differences between the various approximately-equal signs "≈", "≃", and "≅"? The Unicode standard lists all of them inside the Mathematical Operators B...
This approach uses the chinese remainder lemma and it illustrates the "unique factorization of ideals" into products of powers of maximal ideals in Dedekind domains: It follows $-1 \cong 10-1 \cong 9$ hence you get a ...
Jan 1, 2025 · I went through several pages on the web, each of which asserts that $\operatorname {Aut} A_n \cong \operatorname {Aut} S_n \; (n\geq 4)$ or an equivalent statement without proof, and many of them seem to...
Jun 16, 2024 · Another injective cogenerator is the injective hull of the residue field $E (k)$. How this two injective cogenerators are related in general? Is it true that $M \cong E (k)$? If not in general for what ...
Prove that $\mathbb Z_ {m}\times\mathbb Z_ {n} \cong \mathbb Z_ {mn}$ implies $\gcd (m,n)=1$. This is the converse of the Chinese remainder theorem in abstract algebra.
Nov 5, 2023 · A tempting cleaner-looking way would be to observe that $\mathbb {Z} [X]/ (X^n,X-p)\cong \mathbb {Z}/ (p^n)$ and take the inverse limit. I don't see a way to make that work purely formally, though, since...
Originally you asked for $\mathbb {Z}/ (m) \otimes \mathbb {Z}/ (n) \cong \mathbb {Z}/\text {gcd} (m,n)$, so any old isomorphism would do, but your proof above actually shows that $\mathbb {Z}/\text {gcd} (m,n)$ $\tex...
Feb 15, 2015 · A few points on the definition of "simple": 1. Every mono (and epi) is regular in an abelian category, so no need to worry about that. 2. The zero morphism $0 \to X$ is always mono, so you need to say t...
Feb 6, 2025 · The proof given for the theorem is the following: "The description of line bundles in terms of their cocycles provides us with an isomorphism $\operatorname {Pic} (X) \cong \check {H^1} (X,\mathcal {O}^*_X) $ ".