# Origin of “Woodin cardinal”

Sorry if this is a completely stupid question (I'm a not a set-theorist, though I've been doing some reading in the subject), but I was wondering, specifically, about the exact provenance of the name. I know, of course, that it's after Woodin himself, but who coined it? Where is its first appearance in the literature? Just curious.

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@quid Thank you for adding those tags - as a new user here, I was worried about being too liberal with them. –  Michael D. Feb 16 '14 at 23:30
@Asaf Thank you very much as well. –  Michael D. Feb 16 '14 at 23:31
I believe that it first appeared in the Martin-Steel about projective determinacy or so. –  Asaf Karagila Feb 16 '14 at 23:32
No room for the etymology tag? –  Dag Oskar Madsen Feb 16 '14 at 23:33
You are welcome. When in doubt rather use too many than too few tags. See meta.mathoverflow.net/questions/1075/… for some general info on tagging; note especially the inof on top-level tags. –  quid Feb 16 '14 at 23:34

The notions of Shelah cardinals and Woodin cardinals were introduced by Shelah and Woodin in their joint paper

Large cardinals imply that every reasonably definable set of reals is Lebesgue measurable. Israel J. Math., 70 (3), (1990), 381–394. MR1074499 (92m:03087),

which itself was the result of the hugely influential Martin's Maximum paper by Foreman, Magidor, and Shelah. In their "Lebesgue measurable" paper, Shelah cardinals are those $\lambda$ that satisfy property $\mathrm{Pr}_a(\lambda)$, and Woodin cardinals are those that satisfy $\mathrm{Pr}_b(\lambda)$. Overall, the current notation seems better. To get an idea of how quickly the term was adopted, already the Shelah-Woodin paper mentions it, see page 384 and Definition 4.1 in page 392:

We define here two large cardinals: $\mathrm{Pr}_a(\lambda,f)$, $\mathrm{Pr}_a(\lambda)$ by Shelah (Definition 3.5) and $\mathrm{Pr}_b(\lambda)$ by Woodin -- now called a Woodin cardinal.

Note that, in spite of its publication date, the results of the paper were obtained quickly after the results in the Martin's Maximum paper, itself published in 1988. In the $\mathsf{MM}$ paper, we read (page 27)

Woodin, aware of [Foreman's work on $\mathfrak c$-dense, normal, fine ideals on $[(2^{\aleph_0})^+]^{\aleph_1}$] and of Theorem 12 [that $\mathsf{MM}$ implies the saturation of the nonstationary ideal], proved the following proposition. It was proved simultaneously with the third author's realization that this technique of $S$-complete forcing could be used together with the results of Sections 1 and 2 to prove Theorem 21 [on versions of $\mathsf{MM}$ comaptible with $\mathsf{CH}$]. In a phone call to the first author, Woodin, unaware of Theorem 21 and its consequences, announced his proposition.

Woodin's result indicates how to prove from large cardinals that $L(\mathbb R)$ is (elementarily equivalent) to the $L(\mathbb R)$ of a Solovay's model. Working on optimizing this result led to the notions of Shelah and Woodin cardinals.

The relevance of Woodiness was quickly seen in the context of homogeneously Suslin sets, relevant to determinacy, which led to the immediate adoption of the notion.

The first appearance of the term in the literature is in the papers by Donald A. Martin and John R. Steel,

Projective determinacy. Proc. Nat. Acad. Sci. U.S.A., 85 (18), (1988), 6582–6586. MR0959109 (89m:03041),

and

A proof of projective determinacy. Journal of the American Mathematical Society, 2 (1), 1989, 71-125. MR0955605 (89m:03042).

Both terms "Woodin cardinals" and "Shelah cardinals" are probably due to them, but due to the influence of the concept, the terms were in use, particularly Woodin cardinals, before the papers appeared.

For somewhat more precise dates, I suggest looking at

John R. Steel. What is … a Woodin cardinal? Notices Amer. Math. Soc., 54 (9), (2007), 1146–1147. MR2349534.

Steel mentions 1984 for the isolation of the concept of Woodinness, and 1985 for the proof of projective determinacy (see column 1 in page 1147).

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Thanks. I have gone through these papers, but was always fuzzy about whether or not the names became attached to the ideas formally in the literature, especially considering (as far as I'm aware of) the great deal of informal activity of the Cabal in years earlier. –  Michael D. Feb 16 '14 at 23:41
Is "Woodiness" (spelled that way) the actual term used by set-theorists in serious writing? Or was that a typo, or a bit of levity? –  bof Feb 17 '14 at 5:41
@bof I'm pretty sure Andres meant 'Woodinness' (that extra 'n'). In fact, the term appears in the Martin-Steel paper, which, according to Andres' generous answer, is the source-paper I was wondering about. –  Michael D. Feb 17 '14 at 6:14
@bof Typo.${}{}$ –  Andres Caicedo Feb 17 '14 at 6:49