Arthur Fischer
Reputation
98/100 score
 Nov 6 revised Given a square matrix $A$, both $AA^T$ and $A^TA$ are symmetric no longer untagged Nov 6 revised What is meant by a “diagonalization argument”? no longer untagged (but with only a crappy tag) Nov 6 revised Given $f : X \to Y$, then $f^{-1}(f(X)) = X$ no longer untagged Nov 6 revised Proving “if and only if” statements added 9 characters in body; edited tags; edited title Nov 6 revised If $a_n \to L$ and $b_n$ lies between $a_n$ and $a_{n+1}$ for all $n$, then $b_n \to L$ no longer untagged Nov 6 revised Show that $\frac{n(n-1)(n-2)\cdots(n-r+1)}{r!}=\frac{n!}{r!(n-r)!}$ = The binomial coefficient formula we got rid of (proof-strategy) Nov 5 revised Recognizing genuine proof obstructions edited tags Nov 5 revised The square root of a prime number is irrational mainly, removing "proof-strategy" tag; other fixes Nov 5 revised The number $\frac{1}{\sqrt{5}}\left[\left(\frac{1+\sqrt{5}}{2}\right)^{n}-\left(\frac{1-\sqrt{5}}{2}\right)^n\right]$ is always an integer added 294 characters in body; edited tags; edited title Nov 5 revised Under what conditions on $a,b,c,d$ will the function $f(x) = \frac{ax+b}{cx+d}$ be one-to-one on its domain? mainly, removing "proof-strategy" tag Nov 5 revised Two homologous but not homotopic loops on a closed surface of genus greater than one mainly, removing "proof-strategy" tag Nov 5 revised The connection between mathematical induction and implication replaced (proof-strategy) tag with (induction) Nov 5 revised A miscellany of questions about divisibility and gcd added 25 characters in body; edited tags; edited title Nov 5 comment A miscellany of questions about divisibility and gcd I'm voting to close this question as off-topic because it consists of multiple questions which should be asked separately. Nov 5 revised The set of real numbers is a subset of the set of complex numbers? added 16 characters in body; edited tags; edited title Nov 5 revised If $B \setminus C \subseteq A^\text{c}$, then $A \cap B \subseteq C$ deleted 121 characters in body; edited tags; edited title Nov 5 revised Permuting letters within three-letter substrings of strings over $\{\mathsf{x},\mathsf{y},\mathsf{z}\}$ to yield a target “cyclic string” added 519 characters in body; edited tags; edited title Nov 5 revised Given a family $\mathfrak{F}$ for sets, when are $\bigcup \mathfrak{F}$ and $\bigcap \mathfrak{F}$ empty? deleted 25 characters in body; edited tags; edited title Nov 5 revised Using “proof by contradiction” to show that no integer can be both odd and even mainly, removing "proof-strategy" tag Nov 5 revised $5^n > n+4^n$ for all $n\ge2$ mainly, removing "proof-strategy" tag