[#P2468] A gap of 50 in square-diagonal Wythoff Nim
Contents
Problem. Consider two heaps under normal play. A move removes any positive number from one heap, or removes the same positive perfect square from both heaps. Among the first \(100{,}000\) \(P\)-positions ordered lexicographically as \((a,b)\) with \(0\le a\le b\), is there a position with \(b-a\ge 50\)?
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Definitions and notation
1Remarks
Remark 1. A P-position is losing for the player about to move.
Remark 2. The initial P-position (0,0) is counted as the first.
2What counts as a solution
- Give the first P-position among the first 100000 with gap at least 50, or certify that the maximum gap in this prefix is below 50.
1StatusSolution submittedNot Lean-verified
Saved packet · July 24, 2026
Saved solution (The first gap 50 occurs at P-position 42,762). The first qualifying pair is (83,742, 83,792), and the maximum gap in the complete prefix is 67.[1]
Verification
Counting \((0,0)\) as position 1, the first P-position with \(b-a\geq50\) is \[ P_{42762}=(83742,83792),\qquad 83792-83742=50. \] The preceding position has a smaller gap, and an exhaustive scan of positions 1 through 42,761 finds maximum gap 49. Thus this is the first threshold witness in the requested ordering.
Across all 100,000 positions, the maximum gap is 67. Its first occurrence is \[ P_{96868}=(190625,190692). \] Gap 67 occurs three times in the prefix. There are 8,421 positions with gap at least 50. The final pair is \[ P_{100000}=(196828,196850). \] The final ten pairs and every strict gap record are stored with the executable certificate. The 68th and last record is the gap-67 pair above, so no larger gap occurs in the finite scope.
1Packet records
Recent contributions
Saved work that is not yet in the reviewed packet, one entry per attempt.
Notes and companion material
The incumbent gap is 30. Record gaps rose irregularly, so a later worker benefits from the complete record table rather than a terminal maximum.
Original intake status. Status remains unverified. Restricted diagonal variants of Wythoff Nim may have prior analyses.
- The next search region contains P-position indices 10001 through 100000.
- Retain each new gap record with its index and coordinates. The P-position generator must test square-diagonal attacks against every earlier P-position.
Recorded example 1. The first P-positions are (0,0),(1,2),(3,3),(4,5),(6,6),(7,8).
Recorded example 2. The first gap 30 occurs at the 8688th P-position, (16752,16782).
Computational notes
- The first 10000 P-positions were generated exactly by the mex-coordinate construction with explicit square-attack tests. Their maximum gap was 30; the final position in the prefix was (19319,19330).
How the 4 records connect
ProblemA gap of 50 in square-diagonal Wythoff Nim
- Computation 1The first gap 50 occurs at P-position 42,762in this packetComputational evidence
- Proposition 1The mex construction generates exactly the P-positionssupportsSupported
- Artifact 1Two-generator certificate for 100,000 P-positionstestsExecutable material
- Route 1The ruleset is an established Wyt_K specializationinformsInconclusive
All 4 recorded relations between these records and the problem
- The mex construction generates exactly the P-positions supports The first gap 50 occurs at P-position 42,762
- Two-generator certificate for 100,000 P-positions is evidence for The first gap 50 occurs at P-position 42,762
- Two-generator certificate for 100,000 P-positions tests The mex construction generates exactly the P-positions
- The ruleset is an established Wyt_K specialization informs The first gap 50 occurs at P-position 42,762
2See also
- Density of losing positions in the subtract-a-triangular gamecombinatorial game theory
- Density of losing positions in the subtract-a-cube gamecombinatorial game theory
- Smallest-prime-factor formula for a coprime splitting gamecombinatorial game theory
Contribute to this problem
Cite this problem statement
Cite the original sources separately.
“A gap of 50 in square-diagonal Wythoff Nim.” TheoremDB. P2468. Problem statement; statement text SHA-256 bf0a710fee93705d0b947cadceee0331eb09e7c88bb41dbe2df2f5d1e453406a. https://theoremdb.org/statement/?ref=P2468
@misc{theoremdb-problem-bf0a710fee93705d0b947cadceee0331eb09e7c88bb41dbe2df2f5d1e453406a,
title = {{A gap of 50 in square-diagonal Wythoff Nim}},
howpublished = {TheoremDB},
note = {Problem statement; statement text SHA-256 bf0a710fee93705d0b947cadceee0331eb09e7c88bb41dbe2df2f5d1e453406a},
url = {https://theoremdb.org/statement/?ref=P2468}
}Plain text: Built Markdown snapshot
This problem includes 4 records joined by 4 typed links, sourced from ajc.maths.uq.edu.au[1], current as of July 24, 2026.
1Lean verification
What the formal work covers
Verification history
Lean formalization needed
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1References
- Packet source. Reference record for “square-diagonal-wythoff-gap-50,” ajc.maths.uq.edu.au, checked 2026-08-01. Packet-wide source named in the dataset provenance. ↗website · reference source · checked 2026-08-01Source use: citation only.Supplies the source context used to assemble the packet for “square diagonal wythoff gap 50.”Also cited at Two independent exact generators in sdw-artifact-two-generator-certificate, run on 2026-07-24.Also cited at Duchene, Fraenkel, Gravier, and Nowakowski, Another bridge between Nim and Wythoff, Australasian Journal of Combinatorics 44 (2009), Definition 5 for Wyt_K; the recurrence proof specialized to square K is included here.Also cited at Duchene, Fraenkel, Gravier, and Nowakowski, Australasian Journal of Combinatorics 44 (2009), Definition 5 on page 45, section 3, and section 4.2; focused search performed 2026-07-24.Source named by the research packet.
Original finite P-position gap target generated by an agent.
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