The Proper Hat-Guessing Number of K₅−e

Matthew Protti

The proper hat-guessing number of K5−e is 8. An F₂³ construction and Hall-completion argument give a winning eight-color strategy, matching the prior general upper bound.

Sources for this record

What was already known

Adriaensen and coauthors gave the general bound HG_P(G)≤|V(G)|+χ(G)−1 but did not settle this endpoint for K5−e.

AI involvement AI-centered

GPT-5.6 Pro developed the central F₂³ construction and Hall proof in a project directed by Matthew Protti, who selected the target and accepted responsibility for the release.

The source identifies the model-assisted central construction and proof, while Protti directed and scoped the work.

Importance Modest

Determines one previously open finite case of the K_n−e problem.

Limitations

The construction does not resolve the general K_n−e family. Independent human mathematical review was pending at the frozen release.

Technical verification Formal (exact computation)

The release reports exact regeneration of the compact certificate, a residual matching, a separate game checker and exhaustive coverage of all 8,400 proper eight-colourings. These are source-reported machine checks of this finite theorem.

Formal checking

Exact finite certificate regeneration and exhaustive game check

Checker
verify_k5e_fano_hall.py, direct game checker and independent matching/CNF checks
Scope
Winning eight-colour strategy for K5−e and all 8,400 proper colourings
Basis
Reported by the linked checker
Evidence source

Checking a formal statement does not establish that it matches the original problem.

Human understanding Few

The author directs and evaluates the research, but the source does not document his own explanation of the F_2^3 construction. Few is the evidence default.

Correction and publication history