NikolajK
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 1d comment Pullbacks - question 5.7.2 from Awodey's *Category Theory* Btw. I asked a semi-related question here here. 1d comment Pullbacks - question 5.7.2 from Awodey's *Category Theory* For sure you want to add to the square in the second question (with corners being $X, A, B$ and $A\times_X B$) an arrow $f:Y\to X$. What's eventually asked for is supposed to be a pullback square over $Y$. Ask yourself: What are ways in which the 3 remaining corners could be obtained from the 5 you already got? For the last part, think about what you start with (the diagram in that question) and what you're supposed to use (the diagram in the first question). Use the result of the second to bridge the two. 1d comment Let $f_n(x) =\frac{x}{1+nx^2}$ and what function does this sequence converge to? How come you asked 50 questions on Math SE but don't know the basics of formatting here? 1d comment Is $0.999999999… = 1$? $\neg\neg P\implies P$, yikes. Nov 14 revised Why is there no explicit formula for the factorial? added 108 characters in body Nov 14 answered Why is there no explicit formula for the factorial? Nov 6 awarded Yearling Nov 6 awarded Notable Question Sep 11 comment What is the appropriate method to find the value of $1-1/7+1/13-…$ upto infinite terms? Seems like all sums over $\dfrac{z^n}{(n+\alpha)^\color{red}{1}}$ can be solved like this. Is the Lerch transcendent always manageable when the red number (power of the denominator) is 1? Mathematica gives nice functions in $z$ for all integer $\alpha$ I tried. Sep 11 comment If $[T f](x) = f(x) \cos(x)$, show that $T$ is a linear map. Writing $Tf:=x\mapsto f(x)\cos(x)$ would be more clear than $T(f(x))$. Sep 10 comment It is possible regularize the sum related to Voronoi summation Not sure if it helps in any way, but one observation I make is that $\sum_{k=0}^\infty\frac{1}{1-e^{kx}}=\sum_{k=0}^\infty\sum_{j=0}^\infty e^{kjx}=2\sum_{k=0}^\infty\sum_{j0$. The wolframalpha page explicitly tells you the root too, though.