# Tagged Questions

Questions on the usage and meaning of words in mathematics, the names for mathematical entities, and other such questions.

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### Meaning of “-oid” in mathematical concepts?

Some mathematical concepts are ended with "-oid", such as Matroid, greedoid, groupoid. What does that mean? Do these concepts share something in common? Thanks!
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### Slope of a nonlinear curve at a single point

This part of my microeconomics lesson plan has me baffled. Consider for example the nonlinear continuous and differentiable function Y = f(X) = X 2 + 4. Suppose we want to know its slope at the ...
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### Torsion-free fundamental group.

Is there a name for spaces whose fundamental group has no torsion? And what, if any, are some nice properties of these spaces?
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### A prime poset of ideals

Let $A$ be a ring (commutative unital), and $\mathcal I$ be a nonempty family of proper ideals of $A$. I will say that $\mathcal I$ has property $\dagger$ if for any $\mathfrak a\in\mathcal I$ and ...
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### What is the difference between two variables being proportional versus being directly proportional?

I hear these expressions being thrown around, and realize that "proportional" may also incorporate inverse proportion, but are there any other differences?
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### Term for a group where every element is its own inverse?

Several groups have the property that every element is its own inverse. For example, the numbers $0$ and $1$ and the XOR operator form a group of this sort, and more generally the set of all ...
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### Is the term true? $\frac{\theta}{\theta - 1 } = \frac{1} {\theta-1} + 1$

Why is the following term true? What is the corresponding rule or how is it transformed? $\frac{\theta}{\theta - 1 } = \frac{1} {\theta-1} + 1$ Thanks!!
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### “Base is degenerate IFF its corresponding basis matrix is singular”: degenerate with solution and degenerate without solution?

Statement "Base is degenerate IFF its corresponding basis matrix is singular" is wrong according to my Linear-programming teacher Mat-2.3140 in Aalto University (translated from Finnish here/here) ...
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### Topological Space in which every compact subset is metrizable

Is there an (more or less) established name for the class of topological spaces in which every compact subset is metrizable? This is true for example in (LF)-spaces (inductive limits of Frechet-spaces)...
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### Does this object have a category-theoretic name?

I have morphisms: $$f : A \to B \\ g : B \to C$$ The composition is: $$g \circ f : A \to C$$ In the function $(g \circ f)$ we call $A$ the domain and $C$ the codomain (or range). I'm ...
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### How tuples or rows do usually called in statistics?

Is there a special term for couple of measured values of single event in statistics? This is called record, tuple or ...
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### Using “adjunction” to refer to the act of taking adjoints of operators

I have an especially flabby terminology question. How acceptable is it, in your opinion, to use the word "adjunction" to refer to the process of taking adjoints of operators on a Hilbert space? ...
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### What is the difference between a function and a map? [duplicate]

Possible Duplicate: Is there any difference between mapping and function? I am an aspiring mathematician who just started out. What is the difference between a function and a map? Or are these ...
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### Has this algebraic structure been named or studied?

Apologies if this is is not very well-defined or exposes my ignorance; I know comparatively little about abstract algebra. The structure of certain programming languages can be described with the ...
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### What is WHSSETIT?

I am working through a 7 step statistical procedure for hypothesis testing. Step 7 has a field marked WHSSETIT?. What does this acronym stand for and what is the ...
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### Definition of tautological action

What is the precise meaning of the term 'tautological action' as used for example in this Wikipedia page in the context of semigroup actions? For reference the particular sentence is: "A ...
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### Abbreviations in Combinatorial Graph/Matrix theory

I'm getting started with research in combinatorics. I have come across a reference that uses a great deal of abbreviations. I was able to figure most of them out but there are a few that I can find. ...
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### Set $A$ and Set $B$ in each others closures

Let $A$ and $B$ be sets such that $A\subset \overline B$ and $B \subset \overline A$. Isn't that an equivalent statement to saying that $A$ is dense in the closure of $B$ and that $B$ is dense in ...
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### Properly say superscripts locations

In english: $\bigl(x+y^2\bigr)$ is ('x' plus 'y' squared) $(x+y)^2$ is ('x' plus 'y' squared) How can I make the difference in english between the two?