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Enumerative combinatorics, graph theory, order theory, posets, matroids, designs and other discrete structures. It also includes algebraic, analytic and probabilistic combinatorics.

9 votes
2 answers
314 views

Dividing the edges and diagonals of a polygon among disjoint sub-polygons

Let $P$ be a convex $n$-gon ($n$ is odd and $n \geq 5$). Determine the smallest $m$ such that all edges and diagonals of $P$ can be covered by the edges of $m$ convex sub-polygons of $P$ which …
jack's user avatar
  • 3,153
4 votes
2 answers
228 views

Colouring Positive Integers

Does anyone know any reference or proof for the following problem? Let $m$ and $n$ be positive integers, $m,n \geq 2$. Each positive integer is coloured in one of $m$ different colours. Is it possibl …
jack's user avatar
  • 3,153
3 votes
0 answers
132 views

Permutation of a sequence, such that $y_i+y_{i+1}$ are all distinct

The sequence $x_1, x_2, ..., x_n$ of positive integers contains at least $\frac {2n}{3}+1$ distinct numbers and each of them appears at most three times. How to prove that there is a permutation $y …
jack's user avatar
  • 3,153
6 votes
1 answer
437 views

Minimum number of operations necessary to arrive at any configuration

Let $k \geq 2$ and $N_1, N_2, ..., N_k$ be positive integers. Let $S=\{(a_1,a_2,...,a_k) \in \mathbb{Z}^k:1 \leq a_i \leq N_i\}$ and $A=\{1,2,...,\prod_{i=1}^{k} N_{i}\}$. Given a bijective map $f: …
jack's user avatar
  • 3,153
2 votes
1 answer
191 views

Every element of $A$ and $B$ differ in at least $k$ positions

Let $m,n$ be positive integers, $m,n>1$ and $X = \{(x_1,x_2, ..., x_m) \in \mathbb{Z}^m :1 \le x_i \le n, \forall 1 \le i \le m\}$. $A$ and $B$ are two disjoint subsets of $X$, such that if $a \in A$ …
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  • 3,153