Quasi-forest simplicial complexes and almost Cohen-Macaulay

Abstract

In this paper we study the quasi-forest simplicial complexes and we define the concept of simplicial $k$-cycle (denoted by ${\mathcal{S}}_k$) and simplicial $k$-point (denoted by ${\mathcal{P}}_k$). We show that a simplicial complex $\Delta$ is quasi-forest if and only if it does not have any ${\mathcal{P}}_k$ and any ${\mathcal{S}}_k$ for $k\ge 3$. Furthermore we characterize almost Cohen-Macaulay quasi-forest simplicial complexes. In the end we show that the cycle graph $G=C_n$ is almost Cohen-Macaulay if and only if $n=3,4,5,6,7,8,9,11$.

10 pages