English

Counting Small Induced Subgraphs: Hardness of Symmetry-Based Properties

Computational Complexity 2026-06-30 v1

Abstract

Jerrum and Meeks (TOCT, JCSS 2015) introduced the counting problems IndSub(Φ)\text{IndSub}(\Phi) for fixed graph properties Φ\Phi: Given an input graph GG and kNk\in\mathbb N, count the kk-vertex subsets SV(G)S \subseteq V(G) such that the induced subgraph G[S]G[S] satisfies Φ\Phi. For recursively enumerable Φ\Phi, it is known that IndSub(Φ)\text{IndSub}(\Phi) is either #W[1]-hard or fixed-parameter tractable. A direct classification depending on Φ\Phi however still remains open. In particular, the status was open for the property of graphs without nontrivial automorphisms, also mentioned in a very recent survey on parameterized counting by Roth (Comput.~Sci.~Rev.~2026). This is a natural property that evades all currently known techniques for proving #W[1]-hardness, including a general toolkit based on Fourier analysis that was very recently introduced by Curticapean and Neuen (SODA~2025). In this paper, we show that counting induced kk-vertex graphs without nontrivial automorphisms is #W[1]-hard by constructing ``clique scaffolds'', i.e., problem-specific restrictions of the property that enable a reduction from the kk-clique problem. More generally, we show that for every finite group QQ, counting kk-vertex induced subgraphs with automorphism group QQ is #W[1]-hard.

Keywords

Cite

@article{arxiv.2606.31803,
  title  = {Counting Small Induced Subgraphs: Hardness of Symmetry-Based Properties},
  author = {Radu Curticapean and Mingjun Liu},
  journal= {arXiv preprint arXiv:2606.31803},
  year   = {2026}
}