The Proper Hat-Guessing Number of K₆−e

Matthew Protti

The proper hat-guessing number of K6−e is 10. Two order-sensitive twin rules from a sharply four-transitive action on 11 points satisfy the coordinate-line criterion; Hall completion gives a winning ten-color strategy, matching the general upper bound.

Sources for this record

What was already known

Adriaensen and coauthors proved the general bound HG_P(G)≤|V(G)|+χ(G)−1. The earlier K5−e construction does not settle K6−e.

AI involvement AI-centered

GPT-5.6 Pro developed the repaired twin-rule construction and proof under Matthew Protti’s direction. Protti chose the target, evaluated the result and accepted responsibility for the release.

The model contributed the retained deletion-repair construction and proof under Protti’s direction; stronger autonomy is not documented.

Importance Modest

Determines a previously open member of the K_n−e family.

Limitations

This finite construction does not determine the general K_n−e family. The supplied adversarial reviewer is not identified as a human expert.

Technical verification Formal (exact computation)

A dependency-free verifier reportedly regenerated the 7,920-element action, repairs and 2,880 lines, checked all 181,440 proper colourings and the residual degree bound. The reported adversarial replay supports the finite core.

Formal checking

Exact permutation-group regeneration, exhaustive line/colouring and Hall-degree checks

Checker
K6−e dependency-free verifier and supplied adversarial finite-core replay
Scope
HG_P(K6−e)=10 construction, line criterion and 181,440 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

Protti’s evaluation and review are reported, but no separate human explanation of the order-sensitive repair mechanism is documented. Few is the evidence default.

Correction and publication history