Lower bounds for the covering numbers C(24,14,4) and C(25,15,5)

James Chang

Every family of 14-subsets of a 24-point set that covers every 4-subset has at least 20 blocks, so C(24,14,4)≥20. The Schönheim point-derivation bound then gives C(25,15,5)≥34.

Sources for this record

What was already known

Earlier tables gave weaker lower bounds for these covering numbers. The 25-point bound follows from the new 24-point bound and a known derivation inequality.

AI involvement AI-led

James Chang selected the target and directed an OpenAI Dots campaign. Astra agents developed the contradiction excluding 19 blocks and wrote the original Lean proof; the 25-point derivation is standard.

Agents supplied the core mathematical argument and first formal proof while Chang set the task, directed the campaign and later rewrote the presentation; this is not autonomous research.

Importance Modest

Excludes a 19-block (24,14,4) covering and improves a related 25-point lower bound.

Limitations

These are lower bounds, not exact covering numbers, and they do not decide whether 41 blocks suffice for C(25,15,5). The reported machine check covers both finite-set statements; no complete human mathematical check is documented.

Technical verification Formal (Lean 4 with Mathlib; Comparator proof replay through Lean, NanoDa and con-ron kernels)

Palomar v2 records two matching Finset declarations at commit 401d986 and reported mechanical verification, including Comparator replay through Lean and independent kernels. No human proof check is documented.

Formal checking

Registry v2 reports compared finite-set declarations and mechanical verification at the pinned commit.

Checker
Palomar mechanical verifier and Comparator
Scope
C(24,14,4)≥20 and C(25,15,5)≥34 for finite-set covering families
Basis
Reported by the linked checker
Evidence source

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

Human understanding Full

Chang's later paper and companion exposition explain the central incidence, rigidity and counting mechanism; this documents author understanding without implying independent human verification.

Correction and publication history

2026-10-18 · publication

The AI-found 24-point lower bound and its standard 25-point consequence match the reported machine check.

Read this published revision