arXiv subjects
Publications and source records attributed to Griffin Johnston.
Let $g(n)$ denote the minimum number of peeling sequences among all $n$-point sets in general position in the plane. Dumitrescu and Tóth proved an exponential upper bound with base $12.29$, and Simon subsequently lowered the base to $9.78$. Using the same recursive construction, we prove \begin{equation*} g(n) \le (8+o(1))^n. \end{equation*}
Given a vector $α= (α_1, \ldots, α_k) \in \mathbb{F}_2^k$, we say a collection of subsets $\mathcal{F}$ satisfies $α$-intersection pattern modulo $2$ if all $i$-wise intersections consisting of $i$ distinct sets from $\mathcal{F}$ have size $α_i \pmod{2}$. In this language, the classical oddtown and eventown problems correspond to vectors $α=(1,0)$ and $α=(0,0)$ respectively. In this paper, we determine the largest such set families of subsets on a $n$-element set with $α$-intersection pattern modulo $2$ for all $α\in \mathbb{F}_2^3$ and all $α\in \mathbb{F}_2^4$ asymptotically. Lastly, we consider the corresponding problem with restrictions modulo $3$.
In their classical paper, Erdős, Goodman and Pósa studied the representation of a graph with vertex set $[n]$ by a family of subsets $S_1,\dots, S_n$ with the property that $\{i,j\}$ is an edge if and only if $S_i\cap S_j\neq \emptyset$. In this note, we consider a similar representation of bounded degree $r$-uniform hypergraphs and establish some bounds for a corresponding problem.
A subset $A$ of the integers is a $B_k[g]$ set if the number of multisets from $A$ that sum to any fixed integer is at most $g$. Let $F_{k,g}(n)$ denote the maximum size of a $B_k[g]$ set in $\{1,\dots, n\}$. In this paper we improve the best-known upper bounds on $F_{k,g}(n)$ for $g>1$ and $k$ large. When $g=1$ we match the best upper bound of Green with an improved error term. Additionally, we give a lower bound on $F_{k,g}(n)$ that matches a construction of Lindström while removing one of the hypotheses.