Lessel (2026, arXiv:2610.13562) has hit the single-source concentration cap at three claim-notes — what corroborates her account of the four Renaissance centers with no PI-authored GR textbook?

single-source-capcorroborationgeneral-relativityhistory-of-physicshist-ph

As of this promotion (2026-10-14), three claim-notes rest on Bernadette Lessel's "On the Utility of Textbooks in Understanding the Renaissance of General Relativity" (arXiv:2610.13562, submitted 2026-10-09) — an unrefereed preprint from a single author:

• claim-lessel-2026-renaissance-era-gr-textbooks-are-distinctive-historical-testimony
• claim-lessel-2026-nearly-all-renaissance-center-pis-produced-a-school-textbook
• claim-lessel-2026-renaissance-of-general-relativity-dated-1955-to-early-1970s

That is the single-source concentration cap (sources.md, Cali 2026-07-29: no more than three claim-notes may rest on a single unrefereed primary until at least one independent source corroborates it). No independent source — different author, different venue — has corroborated this preprint; it is five days old at the time of this promotion.

Held finding. Of the research centers Roberto Lalli's 2017 book identifies as Renaissance epicenters, Lessel's paper reports four whose principal investigator produced no school-specific GR textbook: Brussels (Robert Debever & Jules Géhéniau), Stockholm (Oskar Klein), Haifa/Technion (Nathan Rosen — though his student Moshe Carmeli became a prolific GR textbook author from 1977), and Purdue (Frederik Belinfante). Lessel offers this as an interesting counter-case to her main PI-textbook correlation rather than developing it further herself. It was the clear next candidate claim-note before the cap intervened.

The specific verification. What would need to land before this finding can become a fourth claim-note, or before the branch as a whole can go past seedling:

1. Independent corroboration of Lessel's reading of Lalli's center list — ideally a direct read of Lalli's 2017 book, Building the General Relativity and Gravitation Community During the Cold War (Springer), itself. The vault has not read Lalli's book directly; everything it currently knows about his list of centers and PIs comes through Lessel's paraphrase of it.
2. A check of whether Debever, Géhéniau, Klein, or Belinfante in fact published no general-relativity textbook — a negative claim, harder to verify than a positive one, and the kind of gap a library catalogue search or a historian's bibliography could close or complicate.
3. Moshe Carmeli's own bibliography (first GR textbook, 1977) as a smaller, checkable positive claim riding alongside the negative one.

Why it matters. The cap exists because the failure mode is invisible one note at a time: each note here is correctly sourced, correctly seedling, correctly flagged as resting on a single preprint by one author — while the branch as a whole could quietly read as corroborated just because it is internally consistent and the author is careful. Corroboration discharges the cap (record it in the notes' audit_status); contradiction is the more interesting finding and a note in its own right.

Progress, 2026-10-16 (promotion of the 2026-10-15 corroboration capture). Partially answered — item 3 above resolved cleanly; items 1 and 2 remain open.

• Item 3 (Carmeli's own bibliography) is settled: two sources independent of each other and of Lessel confirm his first GR textbook was Group Theory and General Relativity (McGraw-Hill, 1977), not the 1982 Classical Fields — see claim-carmeli-1977-group-theory-and-general-relativity-was-his-first-gr-textbook. The Rosen→Carmeli doctoral lineage is separately reported by Wikipedia (Tier 4, one root) in claim-moshe-carmeli-doctoral-advisor-nathan-rosen-technion-1964.
• Item 1 (a direct read of Lalli's book, Appendix A) is still unreached: SpringerLink sits behind an institutional-login wall. The two freely reachable Lalli-authored overview sources — the MPIWG project page and a 2015 Renn/Blum/Lalli conference-slide deck — describe a 1955 US/Europe-scoped map and name only Princeton, Warsaw, and London as illustrative "charmed circles"; neither confirms nor denies Brussels, Stockholm, Haifa, or Purdue. The slide deck's slide 17 ("Research centers active in subjects related to GR around 1955") is titled as if it carries the actual roster, but its content is most likely a figure (map/table) whose text did not extract through this session's PDF tooling — a tooling gap, not evidence the slide lacks a roster. Per Cali's 2026-10-01 ruling, there is no library route for the paywalled Appendix A; the next move is to find a working-paper version, or a later paper that quotes the appendix's center list, and otherwise say it remains unread rather than retrying the paywall.
• Item 2 (an independent check that Debever, Géhéniau, Klein, or Belinfante published no GR textbook) stayed unresolved and weak: targeted biographical searches found no GR textbook credited to Belinfante (Purdue, per his 1992 Physics Today obituary — the one book it credits him with, A Survey of Hidden-Variable Theory, is about quantum mechanics, not GR), Klein (Stockholm, per MacTutor — correction to the 2026-10-15 capture's framing: MacTutor lists general relativity among Klein's subjects across the 1940s and names one specific 1964 GR paper, which is not the same as his entire GR output being "a single paper"), or Géhéniau (Brussels, per the Mathematics Genealogy Project, which records his doctoral work as quantum theory, not GR). All three are absence-of-evidence from searches that may simply have missed a source, not independent confirmation of Lessel's negative claim — not promoted to a claim-note on that basis.
• Further leads, still open and un-shaed: Scott Walter's Centaurus (2020) review and Tiffany Nichols's BJHS (2019) review of Lalli's book (both paywalled, not fetched), and a Technion in-memoriam CV for Rosen (DNS error on fetch) that could directly settle Rosen's own publication record.