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Aug
30
comment Showing a subset of $S_n$ is a subgroup
@Arcane1729 To clarify, you're right, and I understand the claim. But if the generic strategy of just rearranging $klk^{-1}l^{-1}mnm^{-1}n^{-1}$ were to successfully prove the claim, then it would actually succeed in proving more: that the claim is true for arbitrary groups. Contrapositively, since we know the claim is not true for arbitrary groups, we know that the generic strategy can't possibly succeed. That tells use we need to bring in some facts that are specific to $S_n$, like its relationship with $A_n$ or the cycle decompositions of its elements.
Aug
30
comment Showing a subset of $S_n$ is a subgroup
Rearranging elements and manipulating terms isn't working because the statement is false for an arbitrary group. To prove it for $S_n$, you'll have to apply some special knowledge about $S_n$.
Aug
26
comment Is this GRE math problem wrong?
Manhattan Prep doesn't appear to be affiliated with ETS, so I wouldn't even call this a "GRE math problem".
Aug
25
comment What is the “T” set?
@Spencer Read the section "1.4 Preliminaries and Notation", subsection "Geometry on the $n$-torus", where the notation is defined. Short answer, Qiaochu Yuan is right.
Aug
24
comment Existence of a Rectifiable Piecewise Smooth Path
(Nitpick: $\gamma$ has to be injective.)
Aug
24
answered Use of restriction to disallow aberrant series
Aug
24
comment Use of restriction to disallow aberrant series
@mistermarko It's not a good practice to categorically ban the use of a tool just because novices might misuse it.
Aug
21
comment What algebraic structure do date, temperature, and similar quantities belongs to?
Generally, heaps and torsors.
Aug
20
comment The subset of a set of vectors such the this subset has the points at most extreme values for all dimentions
Got it, but then, your two properties don't hold.
Aug
20
comment The subset of a set of vectors such the this subset has the points at most extreme values for all dimentions
I'm not sure if the definition is stated the way you want. What is $Out(\{(1,0),(2,0),(3,0)\})$ meant to be?
Aug
20
comment Open Set in the Cartesian plane.
"My attempt is based in to set $\epsilon=\min\{x_{1}-x,x_{2}-(1-x)\}.$" What is $x$ in this equation?
Aug
19
comment Type(s) of Hashing function that keeps the ordering information
The most significant part of some data is the part that most affects the sort order. For a five-digit number 11323, the first three digits 113__ are more significant than the last two digits ___23. The exact amount of data recoverable from a hash depends on the length of the hash.
Aug
19
comment Type(s) of Hashing function that keeps the ordering information
If the hash function is order-preserving, and an attacker knows the hash function and hash(X), then they can recover the most significant part of X by binary search. Is that acceptable?
Aug
19
answered What is the corresponding term for center of mass for a two-dimensional shape?
Aug
17
comment Condition inverse $p$-adic number
$(a,b)$ is the greatest common divisor of $a$ and $b$.
Aug
17
answered Is frequency a scalar quantity?
Aug
17
answered Condition inverse $p$-adic number
Aug
17
answered Vector spaces $V=-V$
Aug
16
answered Is $\log(-1)$ equal to $-\log(-1)$
Aug
15
comment A box contained within larger box has a smaller surface area than the larger box?
Come to think of it, equation 4.17 gives an even shorter proof: We can probe the surface with lines and count the number of intersections. That might be easier to grok.