Ari Brodsky
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 Mar1 comment Let A and B be sets, then if A ⊆ B then A ∩ B = A I think you've reversed $\subseteq$ and $\supseteq$. Sep23 comment The myth of no prime formula? @mathh Your \exists should be \nexists. Sep9 comment Can't find mistake in an easy proof. @Frunobulax corrected now. Sep9 comment How to solve this limits question For this solution to be correct, you need to show that the original expression is an indeterminate form $\infty/\infty$, which is not completely obvious from the expression as written. Sep9 revised Can't find mistake in an easy proof. fix variable names Sep9 suggested approved edit on Can't find mistake in an easy proof. Jul29 awarded Organizer Jul29 revised Separable differentiable equations replace missing = sign; replace improper-integrals tag with differential-equations tag Jul29 suggested approved edit on Separable differentiable equations Jun12 comment Why infinity multiplied by zero was considered zero here?! While this explains the convergence, it doesn't really answer the OP's question, which was how the ratio test works in this case. The correct answer seems to be this one Jan8 comment Pedagogy: How to cure students of the “law of universal linearity”? More to the point, you have to be able to deal with non-integer exponents. Jan8 comment Pedagogy: How to cure students of the “law of universal linearity”? @JoshuaTaylor How is it different from $3(a+b) = a+b+a+b+a+b = a+a+a+b+b+b = 3a+3b$? Oct1 comment Does a red/blue coloring of the infinite subsets of $\mathbb{N}$ necessarily give an infinite monochromatic $M\subset \mathbb{N}$? Interesting that your answer relies on the cardinality of $\mathbb N$, which the other answers don't. Your answer extends to sets up to size $\mathfrak c$, but not larger. I still like your answer, nevertheless. Sep12 awarded Commentator Sep12 comment Is $\{\emptyset\}$ a subset of $\{\{\emptyset\}\}$? What you are really noticing when you look at the form is that "the set $\{\{\emptyset\}\}$" contains the element $\{\emptyset\}$. $\{\emptyset\}$ is an element of $\{\{\emptyset\}\}$, not a subset of it. Sep2 comment Slice of pizza with no crust In the mathematical formulation, you don't say anywhere that the subsets $A_i$ should be pairwise disjoint (or even almost pairwise disjoint). That would seem to be essential; otherwise the problem might be trivial. Sep2 comment Slice of pizza with no crust I wonder how the mathematical formulation is "more concrete" than the physical description of the problem! May24 comment Topology of the power set Current link is here. (I would have edited it into the answer but the system won't allow me to change just one character.) May6 revised Why is it important to study combinatorics? fixed typo "Brauer" -> "Brouwer" Mar8 comment What was the first bit of mathematics that made you realize that math is beautiful? (For children's book) There was a song about this on Square One TV years ago: "Nine Nine Nine" with the refrain "Nine nine nine, that crazy number nine. Times any number you can find, it all comes back to nine!"