# tohecz

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bio website kmlinux.fjfi.cvut.cz/… location Prague, Czech Republic age 27 member for 2 years, 2 months seen 21 hours ago profile views 133

Math PhD student at Czech Technical University in Prague and at LIAFA in Paris. At the same time, I'm a typesetter (and partly the copy editor) of one scientific journal (done in LaTeX, of course).

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# 338 Actions

 Sep30 awarded Explainer Sep29 comment Is the perimeter of a nested convex set smaller than the containing set's? @Martín-BlasPérezPinilla Damn, my fault. Sorry for that. Sep20 comment Proof my by mathematical induction $\sum_{i=1}^{n} \frac{(-1)^{i-1}}{i} > 0$ Hello, is really your summand independent of $i$? Because currently the sum evaluates to $(-1)^{n-1}$, which is not always positive... Sep19 comment Are $10\times 10$ matrices spanned by powers of a single matrix? +1 Indeed a very nice proof by contradiction. Sep19 answered If A is a matrix, what does A' mean? Sep5 comment Can an observed event in fact be of zero probability? @Did however, the question was on iid $[0,1]$. Sep5 comment Can an observed event in fact be of zero probability? @Aahz No, the fact that you observed it once doesn't mean you'll observe it again later. Aug31 comment Why induction cannot be used for infinite sets? Hello! Could you please tell us where the problem comes from and what have you tried to solve it? Aug31 comment Does the string of prime numbers contain all natural numbers? I love that you have two solutions here: you show that every $k$ is a prefix of a prime written in the decimal system, the other answer shows that every $k$ is a suffix of it :) Aug23 comment Make $n$ cents with $1$-cent, $2$-cent, and $3$-cent coins Well, citing the question: Is there a way to do this without making use of a generation function? Aug23 comment Make $n$ cents with $1$-cent, $2$-cent, and $3$-cent coins That still uses generating functions though, only simplifies the argument. Aug22 suggested rejected edit on If $A$ and $B$ are closed subsets of the set of real numbers, then is $A+B$ closed? Aug22 revised Make $n$ cents with $1$-cent, $2$-cent, and $3$-cent coins improved MathJaX formatting Aug22 suggested approved edit on Make $n$ cents with $1$-cent, $2$-cent, and $3$-cent coins Aug22 answered Make $n$ cents with $1$-cent, $2$-cent, and $3$-cent coins Aug22 comment Make $n$ cents with $1$-cent, $2$-cent, and $3$-cent coins @Ragnar That gives a generalized Tribonacci sequence, which is much more than $\sim n^3/12$. Aug22 comment Make $n$ cents with $1$-cent, $2$-cent, and $3$-cent coins Well, then the answer can't be correct since even with only 1c and 2c coins, there are $f_n$ (Fibonacci number) solutions; that's exponential, not polynomial. Aug22 comment Make $n$ cents with $1$-cent, $2$-cent, and $3$-cent coins Are $5=1+2+2=2+1+2=2+2+1$ three different solutions? It seems not, but I'm not sure Aug17 comment Is there an interval notation for complex numbers? @Teepeemm It's not interval arithmetics, it's simply set arithmetics with addition and multiplication, and you can do this over any ring, right? Aug17 comment Is there an interval notation for complex numbers? @JimmyK4542 It is common to define $X+Y = \{x+y:x\in X, y\in Y\}$ IMHO. There's no need to introduce an extra symbol for that.