On 021-Avoiding Ascent Sequences

[摘要] Ascent sequences were introduced by Bousquet-Mélou, Claesson, Dukes and Kitaev in their study of $(\bf{2+2})$-free posets. An ascent sequence of length $n$ is a nonnegative integer sequence $x=x_{1}x_{2}\ldots x_{n}$ such that $x_{1}=0$ and $x_{i}\leq {\r

[学科分类] 离散数学和组合数学