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Showing positive definite quadratic forms give the "most symmetrical" metrics over $\mathbb{R}^n$
I was unsatisfied with the many proofs of the Pythagorean theorem in which it's not clearly apparent which axioms are specifically needed, or because said axioms seem too geometrically motivated in ...
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Why do $\lim_{b\to \infty} \sqrt{c}-b=\frac{a}{2}$ when $c=b^2+ab$
I've been studying the properties of rectangles for a little while on my own so I don't know what are the actual terms or what are the formulas, but I've noticed that if you take $A$ as a "degree ...
1 vote
1 answer
14 views
Characterization of the $\sigma$-ideal generated by wandering sets for a measureable system $(X,\mathcal{B},T)$
Let $(X, \mathcal{B}, T)$ be a measureable dynamical system, meaning that $T : X \rightarrow X$ is a Borel automorphism over a standard Borel space $(X, \mathcal{B})$. A measureable set $W$ is called ...
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1 answer
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I'm struggling with a logic problem and need some help understanding my mistake
The Problem A duck has two legs. When a duck folds one leg, only one leg is visible. When a duck is sitting, neither of its legs is visible. When Roman went to the lake, there were 33 ducks. He ...
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Computing the Positive Real Zero of the Symbolic Antiderivative of the Riemann-Zeta Function
Taking the indefinite integral of the infinite series definition of the Riemann-Zeta function gives this generalized antiderivative: $$ \int\sum\limits_{n=1}^\infty \frac{1}{n^x} dx = x - \sum\limits_{...
3 votes
1 answer
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Dirac Delta question: does $\int_{-\infty}^{\infty}f(t)\,\delta(t-\tau)\,\mathrm dt=\int_{-\infty}^{\infty}f(t)\,\delta(\tau-t)\,\mathrm dt$? [duplicate]
For a recent project, I have had to read a little bit about linear time invariant systems. In the process of educating myself, I, of course, was introduced to the Dirac delta functional/distribution, $...
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43 views
Are there infinitely many odd composite numbers with digit-disjoint factorizations?
I've been playing around with an idea about composite numbers and the digits of their factors. I've noticed a certain pattern, and for lack of a better term, I've started calling numbers that exhibit ...
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CW-structure on $ X = S^1\times\partial D^2 \;\cup\; \{x,y\}\times D^2 \subset T=S^1\times D^2. $
Considering the space, $ X = S^{1} \times \partial D^{2} \,\cup\, \{x, y\} \times D^{2}. $ the subspace of the solid torus $ S^{1} \times D^{2} $ given by the union of the boundary of the boundary ...
2 votes
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37 views
Contractibility of topological embeddings
The space of smooth embeddings of a manifold $M$ into $\mathbb{R}^\infty$ is contractible by the Whitney embedding argument. Question: Is the space of topological embeddings of a manifold $M$ into $\...
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In how many ways a mouse can get in the $j$-th cell in the $i$-th row?
Suppose we have the following structure: there is $1$ cell in the first row, $2$ cells in the second row, ..., $k$ cells in the $k$-th row, ... (first picture): A mouse stays in the cell in the first ...
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Estimates in Hahn decomposition for measures of finite positive variation
(Hahn decomposition theorem) Let $\mu$ be a signed measure. Then one can find a partition $X = X_+ \cup X_-$ such that $\mu\downharpoonright_{X_+} \geq 0$ and $\mu\downharpoonright_{X_-} \leq 0$. A ...
2 votes
1 answer
56 views
Is this set of Diophantine equations independent?
I have the following eleven equations, where each variable is a positive integer: \begin{align} b-c &= 2u^2 \\ b+c &= 4v^2 \\ b-2c &= w^2 \\ d-a &= 2r^2 \\ d+a &= 4s^...
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On the dimension of linear system to give embedding in $\mathbb{P}^3$
On p. 353 of Algebraic Geometry, Hartshorne poses the question of whether a curve of degree $7$ with $g=5$ exists in $\mathbb{P}^3$. He then says ``We need a very ample divisor $D$ of degree $7$, with ...
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Propositional Logic - Is my simplification correct?
The problem statement is: $A \land B \land A \land (B \lor C) \lor B \land (B \lor C)$ and my solution is $ = A \land B \land A \land (B \lor C) \lor (B \land (B \lor C))$ => Now since $(B \land (...
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92 views
How many points are needed to cover a whole lattice?
Let $p, q\in n^2 = \{0, 1, \dots, n-1\}^2$ be points on the plane. Say "$p$ covers $q$" if the line segment from $p$ to $q$ intersect $n^2$ in no points other than $p$ or $q$ (they are in '...