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The Merrifield-Simmons conjecture also holds for parity graphs

The Merrifield-Simmons conjectures states a relation between the distance of vertices in a simple graph $G$ and the number of independent sets, denoted as $σ(G)$, in vertex-deleted subgraphs. Namely, that the sign of the term $σ(G_{-u}) \cdot σ(G_{-v}) - σ(G) \cdot σ(G_{-u-v})$ only depends on the parity of the distance of $u$ and $v$ in $G$. We prove this statement in the case of parity graphs and give some evidence that this result may not be further generalized to other classes of graphs.