# Tagged Questions

Question on the meaning, history, and usage of mathematical symbols and notation. Please remember to mention where (book, paper, webpage, etc.) you encountered any mathematical notation you are asking about.

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### What does the subscript after euclidean distance notation mean?

Math noob quesetion: What does the "2" subscript mean in the picture below?
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### How to denote the comma as an element of a set

I have a set whose elements include the comma character ",". But the comma is used as a separator when listing the elements of a set. Any suggestions for a sensible notation to use in this case?
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### Defining a singleton in $[0, 1]$

I have seen a singleton in the [0,1] set defined as: $\{b\}=\bigcap\limits_{n=1}^{\infty}(b-1/n, b+1/n] \,\cap\,\Omega$ I am trying to learn some set theory in connection to the need for probability ...
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### Does $\sin(2x)^2 = \sin(2x^2)$ or $(\sin(2x))^2$

In the notation $\sin(x)^2$ Does this equal $\sin(x^2)$ or $(\sin(x))^2$ ? I'm sorry this is such a simple question but Google is unhelpful. There are plenty of sources illustrating $\sin^2(x)$ =...
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### “standard co-deviation”

This is a terminology/notation question. I swear I've seen covariance matrices written as \begin{bmatrix} \sigma_x^2 & \sigma_{x,y}^2 \\ \sigma_{y,x}^2 & \sigma_y^2 \end{bmatrix} Given ...
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### A monoid where every element has finitely many divisors

Is there a special name or has there been any study of monoids of this form? This came up in considering the general construction of a multivariate power series algebra over a ring $R$; usually we ...
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### What is difference between notations a|b and a/b?

I am just a beginner. Can somebody tell me what is the exact difference between these notation, if any? $a|b$ and a/b
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### A question about Game Theory Notation in symmetric Games

In Martin Osbourne and Ariel Rubenstien's book A Course In Game Theory (page 20) the authors say that a 2 person game is symmetric the A1 = A2 (both players have access to the same action set) and (...
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### What is the correct (i.e., precise) term for a vector of the form $(a_1,…,a_n)$?

What is the correct (i.e., precise) term for a vector of the form $(a_1,...,a_n)$? I ask this because my definition of vector is that it is an element of some vector space, this means that whenever ...
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### Are choice function and axiom of choice equivalent?

Axiom - True for all $X:$ if $X \neq \emptyset,$ then there's some $f: X \to \cup X$ such that for any $A \in X, f(A) \in A.$ But the axiom above looks very much like the choice function. Are they ...
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why is this expression valid? $c_{i}(x_{i}+y_{i})$ it has the index repeated 3 times instead of 2 times.
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### Notation for the set $\{1,2,..,k\}$

I often find myself using the set $\{1,2,..,k\}$, sometimes on multiple occasions in a sentence. I've been told that $[k]$ is a short notation for this, but have never seen that in use. Could someone ...
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### In math notation, how to indicate that one number is supposed to be appended/prepended to (or inserted in) another number as a whole?

I don't know if there exists a special, separate term for this operation in mathematics (maybe "to ascribe"?), but here is an example. Let's say I have a variable $m=2$ and I want to write it at the ...
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### First Order Logic Question - “All cats either love or hate dogs.”

Given the following set of predicates: $$\{cat(x), dog(x), love(x, y), hate(x, y)\}$$ How would you transform the following English statement into First Order Logic... Statement: "All cats either ...
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### Autoconvolution Notation

Is there any special notation for a list (or function) convolved with itself? For example, the convolution of the list [1,1,1,1] with itself produces a new list: [1, 1, 1, 1] * [1, 1, 1, 1] = [1,...