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bio website blog.plover.com
location Philadelphia, USA
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visits member for 2 years, 4 months
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I am Mark Dominus, an amateur.

I have a blog that often carries articles about mathematics.


1d
revised Union and Intersection of sets
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1d
revised Pirates And Coins No.1
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1d
comment Pirates And Coins No.1
Wikipedia
1d
revised Primary school math regarding circles
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1d
comment Formal Notation - A simple example
It might be worth noticing separately that $\{ d \mid d\in S\}$ is nothing more than a complicated way to write $S$.
2d
comment SAT Algebra and elementary number theory
In question 1, $a$ could be $6$ and $b$ could be $1000$, right? Then (i) is not true. Something that might help make this kind of question clearer is to reformulate it about money instead of about abstract numbers. Suppose you know that Alice has more than \$5 and Bob has more than \$4. Do you know that Alice has more than Bob?
2d
revised Can any collection of open sets in $\mathbb{R}$ be covered by a countable subcollection?
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2d
revised Fact about limit
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2d
revised Which of $\varphi$ or $\lnot \varphi$ can be expressed by using only the $\rightarrow$ connective?
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2d
comment Which of $\varphi$ or $\lnot \varphi$ can be expressed by using only the $\rightarrow$ connective?
@GitGud I think the $\varphi =$ can be disregarded; I guess that the original question had the form “Write a proposition equivalent to $\varphi$ using only the $\to$ connective”. It is not clear that the asker of the question considers $\lnot$ to be a connective.
2d
answered Which of $\varphi$ or $\lnot \varphi$ can be expressed by using only the $\rightarrow$ connective?
2d
revised Which of $\varphi$ or $\lnot \varphi$ can be expressed by using only the $\rightarrow$ connective?
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Jul
9
comment Why do probabilists have a preoccupation with urns?
It strikes me as remarkably obtuse to demand an explanation for why Italian urna was translated as English "urn". An explanation might be required if urna had been translated as anything else.
Jul
9
revised Does a finite game that cannot be drawn imply a winning strategy exists?
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Jul
9
revised On the nilpotence of the matrix $AB-BA$
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Jul
9
revised What is the use of hyperbolic trigonometric functions if they are easily expressible algebraically?
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Jul
8
comment What is the use of hyperbolic trigonometric functions if they are easily expressible algebraically?
You might also note that $\sin x = \tfrac{1}{2i}(e^{ix} - e^{-ix})$ and $\cos x = \tfrac12 (e^{ix} + e^{-ix})$. So the standard trigonometric functions are also expressible algebraically, almost as simply as the hyperbolic functions.
Jul
8
revised Does a finite game that cannot be drawn imply a winning strategy exists?
Add explanation about drawn positions
Jul
8
revised Conjugates and normalizer
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Jul
8
comment Why do people lose in chess?
I explained the argument in some detail here: Does a finite game that cannot be drawn imply a winning strategy exists?