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 Yearling
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Sep
1
comment If the decimal expansion of $a/b$ contains “$7143$” then $b>1250$
You might have gone through older editions of Bundeswettbewerb Mathematik. In the year 1983 (I think), there was the exact same problem statement with "1983". Actually, it might have been any year between 1980 and 1999 because I remember that $\frac{19}{96}<\frac ab<\frac15$ could be used to show that $b>100$.
Sep
1
answered If the decimal expansion of $a/b$ contains “$7143$” then $b>1250$
Sep
1
comment How is $\mathbb N$ actually defined?
Don't you mean the first countable infinite ordinal?
Sep
1
comment How is $\mathbb N$ actually defined?
If $0$ occurs in your Peano axioms the $0\in\mathbb N$. If you replace $1$ for $0$ in them, then $0\notin \mathbb N$.
Sep
1
comment Solving an equation $x^{22}\equiv2 \bmod 23$
@DietrichBurde not for all $x$.
Sep
1
answered Is the language $L$ generated by 'Fibonacci Strings' (as given in the desciption) regular? If not, disprove by Pumping Lemma
Sep
1
revised Is the language $L$ generated by 'Fibonacci Strings' (as given in the desciption) regular? If not, disprove by Pumping Lemma
added 19 characters in body; edited title
Sep
1
answered What does a left-continuous version of a function mean?
Sep
1
comment What does a left-continuous version of a function mean?
Could it be that $f^-(x):=\lim_{t\to x^-}f(t)$?
Sep
1
comment Let $V=\bigcup_{i=1}^n W_i$ where $W_i$ s are subspaces of a vector space $V$. Show that $V=W_r$ for some $1 \leq r \leq n$.
@user118494 "Let $W_1\cup W_2$ is a subspace of a vector space $V$ iff $W_1\subseteq W_2$ or $W_2\subseteq W_1$." happens to be true alo over finite fields and at any rate cannot readily be extended to $n>2$. Henc $W_1\subseteq \ldots \subseteq W_n$ is not something we already know
Sep
1
answered Number of committees of size 5 with at least 2 women from a society with 10 men and 12 women
Sep
1
revised Product of countably many 1-dimensional spaces does not have cardinality $\aleph_0$
added 12 characters in body
Sep
1
answered Product of countably many 1-dimensional spaces does not have cardinality $\aleph_0$
Sep
1
awarded  Yearling
Aug
31
comment Let $V=\bigcup_{i=1}^n W_i$ where $W_i$ s are subspaces of a vector space $V$. Show that $V=W_r$ for some $1 \leq r \leq n$.
@JyrkiLahtonen That's a really elegant proof for the claim by the way
Aug
31
comment Let $V=\bigcup_{i=1}^n W_i$ where $W_i$ s are subspaces of a vector space $V$. Show that $V=W_r$ for some $1 \leq r \leq n$.
Yes, now you mention that $F$ should be infinite. But where do you use it? More to the point, how do you justify the "from what you already know" (it can't be justified)
Aug
31
comment Let $V=\bigcup_{i=1}^n W_i$ where $W_i$ s are subspaces of a vector space $V$. Show that $V=W_r$ for some $1 \leq r \leq n$.
Where do you use that the ground field is infinite? If you don't your proof must be wrong (because the result is wrong if $|F|\le n$)
Aug
31
comment Is it legal to define a function like this?
If $x\in\mathbb C$, then this is not really a recursion, you are missing the base case(s)
Aug
31
answered Probability of single digits from coin tosses
Aug
31
comment Let $V=\bigcup_{i=1}^n W_i$ where $W_i$ s are subspaces of a vector space $V$. Show that $V=W_r$ for some $1 \leq r \leq n$.
Well, the linked questions have answers with self-contained proofs for the infinite case. So what makes this question a non-duplicate?