A Bivariate $B$-Restricted Clique Polynomial: From Local Neighborhoods to Global Expansion

Let $G$ be a finite simple graph and $B\subseteq V(G)$. We introduce the \emph{bivariate $B$-restricted clique polynomial} $$C_B(G;x,y)=\sum _{\begin{array}{c}K\subseteq V\\ K\text{ is a clique}\end{array}}{x}^{\mathrm{\mid }K\mathrm{\mid }}{y}^{\mathrm{\mid }K\cap B\mathrm{\mid }},$$ where the coefficient of $x^i{y}^j$ counts cliques of size $i$ with exactly $j$ vertices in $B$. This polynomial simultaneously captures combinatorial structure, local extremal properties, and spectral constraints associated with the subset $B$. \ First, we develop vertex and edge deletion recurrences, generalizing classical clique polynomial results. These recurrences imply monotonicity for the largest negative root ${\zeta }_G(B;y)$ (viewed as a polynomial in $x$ for fixed $y\in [0,1]$) under induced and spanning subgraphs. From this, we derive bounds on $B$-independence numbers, $B$-girth, and clique densities restricted to $B$. \ Next, we prove that for any integer $r\ge 1$, any $r$-connected $K_{r+3}$-free chordal graph $G$, and any subset $B\subseteq V(G)$, the bivariate clique polynomial $C_B(G;x,y)$ is real-stable. \ Then, we connect $C_B(G;x,y)$ with spectral graph theory. For $(n,d,\lambda )$-graphs, expansion constraints via Tanner’s inequality limit clique growth within $B$, yielding explicit bounds on coefficients and ${\zeta }_G(B;y)$. \ Finally, we analyze weighted vertices and homomorphism obstructions in this framework, giving a general no-homomorphism criterion. We also conclude the paper with a couple of interesting open problems for young and motivated researchers.