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3 votes
0 answers
118 views

Divide Euclidean space by surfaces

It is well known that $n$ hyperplanes in $\mathbb{R}^k$ can divide $\mathbb{R}^k$ into at most $p$ regions where $p$ is \begin{equation} 1 + n + C^2_n + \cdots + C^k_n \end{equation} Is there similar ...
Hao Yu's user avatar
  • 185
1 vote
0 answers
67 views

Counting pieces when an object is cut n ways

I was reading a passage from an old essay by Martin Gardner on the calculus of finite differences, and it seems to me that there is more that can and should be said about seemingly anomalous values of ...
James Propp's user avatar
  • 19.7k
2 votes
1 answer
153 views

Bounding number of $k$-nearest neighbor sets in $\mathbb{R}^d$

Suppose that $\mathcal{X} \subseteq \mathbb{R}^d$ is compact. Let there be $n$ distinct points $X = \{ x_1,...,x_n \} \subseteq \mathcal{X}$ and $k = \lfloor n^\alpha \rfloor$ where $0 < \alpha &...
heinrich's user avatar
7 votes
0 answers
157 views

How big can a family of pairwise intesecting affine spaces be?

I apologize if this question might seem to be a bit too elementary. Let $\mathbb{P}^n$ be the projective space over $k$ - an algebraically closed field of characteristic 0. Let $1\leq l\leq n-1$, and ...
peter's user avatar
  • 91
6 votes
2 answers
451 views

Up to projectivities, which configurations of four lines in $\mathbb{P}^3$ can one distinguish?

Background I am interested in the projective classification of reduced curves of degree four in $\mathbb{P}^3(\mathbb{R})$ (and more generally of degree $n+1$ in $\mathbb{P}^n(\mathbb{R})$). More ...
Georg M.'s user avatar