Micah Coleman
We present a class of permutations for which the number of distinctly ordered subsequences of each permutation approaches an almost optimal value as the length of the permutation grows to infinity.
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On Two Related Questions of Wilf Concerning Standard Young Tableaux
本文考虑了 Wilf 提出的与标准杨表相关的两个问题，通过纯组合方法对其中一个问题给出部分解答，并由此对另一问题得出更一般的解答。
Permutations Almost Avoiding Monotone Distant Patterns
该研究探讨了几乎避免单调远距离模式的排列，发现Wilf等价性并给出了指数增长速率的新界。
Enumeration of super-strong Wilf equivalence classes of permutations in the generalized factor order
本文通过递归公式枚举广义因子序下排列的超强Wilf等价类，并揭示其与移位等价的联系，从而完整描述并枚举排列的移位等价类。
For a permutation $π$, let $S_{n}(π)$ be the number of permutations on $n$ letters avoiding $π$. Marcus and Tardos proved the celebrated Stanley-Wilf conjecture that $L(π)= \lim_{n \to \infty} S_n(π)^{1/n}$ exists and is finite. Backed by numerical evidence, it has been conjectured by many researchers over the years that $L(π)=Θ(k^2)$ for every permutation $π$ on $k$ letters. We disprove this conjecture, showing that $L(π)=2^{k^{Θ(1)}}$ for almost all permutations $π$ on $k$ letters.
On the growth rate of the Stanley-Wilf limit of blockable permutations
本文研究了可块 permutation 的 Stanley-Wilf 限制的增长率，发现其在特定结构类中呈现多项式增长。
Given coprime positive integers $g_1 < \ldots < g_e$, the Frobenius number $F=F(g_1,\ldots,g_e)$ is the largest integer not representable as a linear combination of $g_1,\ldots,g_e$ with non-negative integer coefficients. Let $n$ denote the number of all representable non-negative integers less than $F$; Wilf conjectured that $F+1 \le e n$. We provide bounds for $g_1$ and for the type of the numerical semigroup $S=\langle g_1,\ldots,g_e \rangle$ in function of $e$ and $n$, and use these bounds to prove that $F+1 \le q e n$, where $q= \left \lceil \frac{F+1}{g_1} \right \rceil$, and $F+1 \le e …
Typical growth of the Füredi-Hajnal and Stanley-Wilf limits
本文证明一致随机置换矩阵的 Füredi-Hajnal 和 Stanley-Wilf 极限以高概率至多为 exp(O(√k(log k)^{5/2}))，改进先前上界，并结合下界表明对数阶为 k^{1/2+o(1)}。
An upper bound for the type of a numerical semigroup, and a reduction of Wilf's conjecture
该研究给出数值半群型的上界，将Wilf猜想归约为不含导子和nn的不等式，确定亏格不等式等号情形，修正相关分类并回答特定问题。
Let S_n denote the symmetric group of all permutations of the set {1, 2, ...,n} and let S = \cup_{n\ge0} S_n. If Pi is a set of permutations, then we let Av_n(Pi) be the set of permutations in S_n which avoid every permutation of Pi in the sense of pattern avoidance. One of the celebrated notions in pattern theory is that of Wilf-equivalence, where Pi and Pi' are Wilf equivalent if #Av_n(Pi)=#Av_n(Pi') for all n\ge0. In a recent paper, Sagan and Savage proposed studying a q-analogue of this concept defined as follows. Suppose st:S->N is a permutation statistic where N represents the nonnegativ…
The symmetric group is generated by σ = (1 2 ... n) and τ = (1 2). We answer an open problem of Nijenhuis and Wilf by constructing a Hamilton path in the directed Cayley graph for all n, and a Hamilton cycle for odd n.
Answering a question of Wilf, we show that if $n$ is sufficiently large, then one cannot cover an $n \times p(n)$ rectangle using each of the $p(n)$ distinct Ferrers shapes of size $n$ exactly once. Moreover, the maximum number of pairwise distinct, non-overlapping Ferrers shapes that can be packed in such a rectangle is only $Θ(p(n)/ \log n).$
Erdős asked the following question: given $n$ points in the plane in almost general position (no 4 collinear), how large a set can we guarantee to find that is in general position (no 3 collinear)? Füredi constructed a set of $n$ points in almost general position with no more than $o(n)$ points in general position. Cardinal, Tóth and Wood extended this result to $\mathbb{R}^3$, finding sets of $n$ points with no 5 on a plane whose subsets with no 4 points on a plane have size $o(n)$, and asked the question for higher dimensions: for given $n$, is it still true that the largest subset in genera…
In this paper, we consider the following problem: what is the minimum number of affine hyperplanes in $\mathbb{R}^n$, such that all the vertices of $\{0, 1\}^n \setminus \{\vec{0}\}$ are covered at least $k$ times, and $\vec{0}$ is uncovered? The $k=1$ case is the well-known Alon-Füredi theorem which says a minimum of $n$ affine hyperplanes is required, proved by the Combinatorial Nullstellensatz. We develop an analogue of the Lubell-Yamamoto-Meshalkin inequality for subset sums, and completely solve the fractional version of this problem, which also provides an asymptotic answer to the integr…
On the math-fun mailing list (7 May 2013), Neil Sloane asked to calculate the number of $n \times n$ matrices with entries in $\{0,1\}$ which are squares of other such matrices. In this paper we analyze the case that the arithmetic is in $\mathbb{F}_{2}$. We follow the dictum of Wilf ("What is an answer?") to derive a "effective" algorithm to count such matrices in much less time than it takes to enumerate them. The algorithm which we use involves the analysis of conjugacy classes of matrices. The restricted integer partitions which arise are counted by the coefficients of one of Ramanujan's m…
On the almost-palindromic width of free groups
本文证明了不存在自然数对(c,m)使得二元自由群的每个元素都能表示为至多c个m-几乎回文的拼接，并将该否定结果推广到所有非阿贝尔自由群，从而回答了Bardakov提出的问题。
The following generalisation of the Erdős unit distance problem was recently suggested by Palsson, Senger and Sheffer. Given $k$ positive real numbers $δ_1,\dots,δ_k$, a $(k+1)$-tuple $(p_1,\dots,p_{k+1})$ in $\mathbb{R}^d$ is called a $(δ,k)$-chain if $\|p_j-p_{j+1}\| = δ_j$ for every $1\leq j \leq k$. What is the maximum number $C_k^d(n)$ of $(k,δ)$-chains in a set of $n$ points in $\mathbb{R}^d$, where the maximum is taken over all $δ$? Improving the results of Palsson, Senger and Sheffer, we essentially determine this maximum for all $k$ in the planar case. error term It is only for $k\equ…
In the present paper, we study the limit sets of the almost periodic functions $f(x)$. It is interesting that the values $r=\inf|f(x)|$ and $R=\sup|f(x)|$ may be expressed in the exact form. We show that the ring $r\leq |z|\leq R$ is the limit set of the almost periodic function $f(x)$ (under some natural conditions on $f$). The exact expression for $r$ coincides with the well known partition problem formula and gives a new analytical method of solving the corresponding partition problem. Several interesting examples are considered. For instance, in the case of the five numbers, the well-known…
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