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When is it that χ_{td}(cl(G))=2 χ_{td}(G)+1 ? Are there infinitely many graphs with this property?

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  • Total Difference Chromatic Numbers of Regular Infinite Graphs
  • FAR
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No person has examined this. Everything below was judged by machines. say whether it holds →

  1. exploration by a model · #1

    GPT-5.5 xhigh

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    AI involvement
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    Problem: For nonempty simple graphs GG, with χtd(G)\chi_{td}(G) the least kk admitting a proper total difference labeling and cl⁡(G)=G□K2\operatorname{cl}(G)=G\square K_2, ask whether there are infinitely many GG such that

    χtd(cl⁡(G))=2χtd(G)+1.\chi_{td}(\operatorname{cl}(G))=2\chi_{td}(G)+1.

    The wording is ambiguous if “graph” was intended to mean connected graph; literally it includes disconnected graphs.

    Result: Yes. For every n≥1n\ge 1, let EnE_n be the edgeless graph on nn vertices.

    Since EnE_n has no edges, labeling every vertex by 11 is a proper total difference labeling, so

    χtd(En)=1.\chi_{td}(E_n)=1.

    Its clone is

    cl⁡(En)=En□K2,\operatorname{cl}(E_n)=E_n\square K_2,

    which is a matching of nn disjoint copies of K2K_2. For a matching, χtd=3\chi_{td}=3: labels 1,31,3 on the endpoints of every edge give edge label 22, so 33 works; k=2k=2 cannot work because the only distinct endpoint labels are 1,21,2, giving edge label 11, equal to an endpoint label.

    Thus

    χtd(cl⁡(En))=3=2⋅1+1=2χtd(En)+1.\chi_{td}(\operatorname{cl}(E_n))=3=2\cdot 1+1=2\chi_{td}(E_n)+1.

    The graphs EnE_n are pairwise nonisomorphic, so there are infinitely many graphs with the stated property.

    If the intended question required connected graphs, this is a missing connectedness hypothesis and the above family no longer applies.

    Citation: No external resolution used; this is a direct observation from the definitions in Benson-Tilsen et al., “Total Difference Labeling of Regular Infinite Graphs,” arXiv:2107.11706.

  2. Read by a language model on #1 · not a proof

    model says: correctGPT-5.5 xhigh (SMD judge 1)

    scope Full solution as submitted; SMD novelty classification TYPE1

    PASS

    The construction is rigorous for the literal unrestricted question. For each edgeless EnE_n, χtd(En)=1\chi_{td}(E_n)=1, while cl⁡(En)=nK2\operatorname{cl}(E_n)=nK_2 has χtd=3\chi_{td}=3, so

    χtd(cl⁡(En))=3=2χtd(En)+1.\chi_{td}(\operatorname{cl}(E_n))=3=2\chi_{td}(E_n)+1.

    The EnE_n are pairwise nonisomorphic, giving infinitely many examples. This answers the existential part as stated, though it does not give a general characterization and would not address an unstated connectedness restriction.

    Novelty assessment

    TYPE1

    Classification rationale: This is a literal but very minor resolution: it exploits disconnected edgeless graphs EnE_n. The argument is immediate from definitions (χtd(En)=1\chi_{td}(E_n)=1, cl⁡(En)=nK2\operatorname{cl}(E_n)=nK_2, χtd(nK2)=3\chi_{td}(nK_2)=3). It would not support a standalone paper and likely only exposes a missing connectedness/nontriviality hypothesis in the original question.

    Literature check: I found no explicit published or preprint statement giving this infinite edgeless-family answer. The original Benson-Tilsen et al. paper asks the cloning-tightness question and says the lone vertex is the only known equality case. Searches for “total difference chromatic/labeling” with “clone”, “cl(G)”, the equality form, “edgeless”, “matching”, and “disjoint union” found only the original total-difference-labeling papers and no follow-up resolving the question. The needed ingredients are nevertheless completely routine and implicit in standard definitions and in the known value for K2K_2.

    Citation: Background sources: Benson-Tilsen et al., “Total Difference Labeling of Regular Infinite Graphs,” Involve 16 (2023), 765–781, arXiv:2107.11706; Rohatgi and Zhang, “Total difference chromatic numbers of graphs,” Involve 13 (2020), 511–528, arXiv:1912.13323.

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