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 Apr 7 answered Picard Group Can Contain rational curve? Feb 5 awarded Citizen Patrol Jan 30 answered Solving Fulton and Harris exercise 2.4 Jan 30 comment Solving Fulton and Harris exercise 2.4 Please provide the exercise number from Fulton–Harris. Jan 23 answered group homomorphisms from the real line to infinite torsion abelian groups Jan 23 comment group homomorphisms from the real line to infinite torsion abelian groups @user66257 — The group $\mathbb{R}$ is a $\mathbb{Q}$-vector space. (Maybe this helps to see why Eric Wofsey's comment is relevant.) Jan 23 comment group homomorphisms from the real line to infinite torsion abelian groups Off-topic: why is there exactly one mathematical symbol in your question that deserves MathJaXification, while all the others have to be satisfied with plain cold sans-serif typesetting? Dec 20 awarded Constituent Dec 19 revised If $G/Z(G)$ is finite, then $|G'| < \infty$ Improves formatting Dec 19 suggested approved edit on If $G/Z(G)$ is finite, then $|G'| < \infty$ Dec 15 awarded Caucus Dec 15 comment Maths to take a user chosen number to a predictable number See en.wikipedia.org/wiki/Collatz_conjecture. Ask them to run the computations until they stabilise. Definitely works for integers $\le 100$, and conjecturely for arbitrary positive integers. (Oops, I just remembered that it always ends in $\ldots,4,2,1,4,2,1,\ldots$; so maybe this is not a very good idea. Dec 15 awarded Critic Sep 30 awarded Explainer Jun 16 comment Irreducibility of $x^n-x-1$ over $\mathbb Q$ @Corvus — To echo TedShifrin, the polynomial ring $\mathbb{F}_{p}[X]$ is infinite, the set $\mathrm{Map}(\mathbb{F}_{p}, \mathbb{F}_{p})$ is finite. Hence the natural map $\mathbb{F}_{p}[X] \to \mathrm{Map}(\mathbb{F}_{p}, \mathbb{F}_{p})$ is not injective. To stress the difference, let me ‘prove’ that $\mathbb{F}_{2}$ is algebraically closed: Take a non-constant polynomial $f$, then $f$ is not constant $1$, and as $\mathbb{F}_{2}$ has only two elements, $f(x) = 0$ for some $x \in \mathbb{F}_{2}$. Thus $f$ has a zero, hence $\mathbb{F}_{2}$ is algebraically closed. $\square$ Spot the error. Jun 3 comment When do we have that Absolute hodge classes= Hodge classes for complex projective manifolds? I think, if the Lefschetz operators are algebraic, then André's motivated cycles are algebraic. May 27 comment A simpler expression that is always smaller or larger Well, write your function as $an^2 + bn + c$, where $a,b,c$ are fractions. Then it is already pretty simple. Next, you can consider if you want your estimate on a particular domain, or on all of $\mathbb{R}$. Depending on the answer, you might be able to round $a$ to an integer, and get rid of $b$ and $c$. May 27 answered A simpler expression that is always smaller or larger May 27 answered Why do the addition of linear equations all pass through the same point May 27 suggested rejected edit on can someone give me the solution with the proof?