Ulam–Kelly reconstruction conjecture for graph homomorphism counts

Let Hom(F,G)Hom(F,G) denote the number of graph homomorphisms from FF to GG, and let G\mathcal{G} be the family of all graphs. For a family of graphs F\mathcal{F}, say that Hom(F,)Hom(\mathcal{F},\cdot) is reconstructible if, for every graph GG with at least three vertices, the vector of homomorphism counts Hom(F,G)Hom(\mathcal{F},G) is uniquely determined by the vectors Hom(F,Gi)Hom(\mathcal{F},G\setminus i) for every vertex ii of GG. Ulam–Kelly reconstruction conjecture. Hom(G,)Hom(\mathcal{G},\cdot) is reconstructible. This is the homomorphism-count formulation of the Ulam–Kelly graph reconstruction conjecture, asserting that a graph with at least three vertices is determined up to isomorphism by the collection of its vertex-deleted subgraphs. The source presents this formulation as a motivation and question; no resolution is given here.

Sources & referencesView supporting material

Primary source

Thomás Jung Spier, “Efficient reconstruction of the characteristic polynomial”, arXiv:2503.17853 (2025).

Additional references

2 papers in this index state this conjecture (2025). The statement above is taken from the most recent of them; the others are arXiv:2502.12781.

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