Rigidity conjecture for generic symmetric hypergraphs

Let n2n\geq 2. Let Ln={R}\mathscr{L}_n=\{R\} be a relational language with RR an nn-ary relation, and let AgeKsym,n\operatorname{AgeK}_{\mathrm{sym},n} be the class of all finite Ln\mathscr{L}_n-structures in which RR is symmetric, meaning that

τSym([n])(x0,,xn1)R(x0,,xn1)R(xτ(0),,xτ(n1)).\bigwedge_{\tau\in\operatorname{Sym}([n])}(\forall x_0,\dots,x_{n-1})\,R(x_0,\dots,x_{n-1})\leftrightarrow R(x_{\tau(0)},\dots,x_{\tau(n-1)}).

For an uncountable cardinal κ\kappa, let Mκ\mathbb{M}_\kappa be the unique structure in the empty language of size κ\kappa, and let GG be generic for the forcing Fn(Mκ)[AgeKsym,n](ω)\operatorname{Fn}(\mathbb{M}_\kappa)[\operatorname{AgeK}_{\mathrm{sym},n}](\omega) over VV. Rigidity conjecture for generic symmetric hypergraphs. The structure G\bigcup G is rigid in V[G]V[G]. This conjecture proposes that the forcing construction yields a symmetric generic hypergraph with no nontrivial automorphisms, despite the absence of function symbols that could name ordered tuples. The corresponding rigidity argument is immediate for sufficiently asymmetric relational structures but does not presently extend to symmetric nn-hypergraphs, so the claim remains open.

Sources & referencesView supporting material

Primary source

Nathanael Ackerman, Mohammad Golshani and Mostafa Mirabi, “Cohen Generic Structures with Functions”, arXiv:2310.11582 (2024).

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