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    • CommentRowNumber1.
    • CommentAuthorUrs
    • CommentTimeSep 5th 2012

    at the beginning of ring I have spelled out a more explicit definition. Also added the examples of rings on cyclic groups to explain the origin of the word “ring”.

    • CommentRowNumber2.
    • CommentAuthorTodd_Trimble
    • CommentTimeSep 5th 2012

    to explain the origin of the word “ring”.

    I didn’t know that! Do you have a source for that?

    • CommentRowNumber3.
    • CommentAuthorUrs
    • CommentTimeSep 5th 2012
    • (edited Sep 5th 2012)

    Do you have a source for that?

    Hm. Let’s see. That’s what they told me when I was a gullible student. I never checked the originals. The entry Mathworld – Ring tells its readers the same story:

    The term was introduced by Hilbert to describe rings like […] By successively multiplying the new element […], it eventually loops around to become something already generated, something like a ring,

    but apparently it’s just a story, not a review of Hilbert’s way of introducing the term.

    Okay, so I went to Google books and read Hilbert’s original article

    David Hilbert, Die Theorie der algebraischen Zahlkörper, Jahresbericht der Deutschen Mathematiker-Vereinigung 4 (1879)

    and there, in section 9.31, indeed no motivation like this is given. Instead it just says:

    […] ein Zahlring, Ring oder Integritätsbereich genannt

    with a footnote that reads

    Nach Dedekind “eine Ordnung”.

    And that’s it. But so that means already that I was wrong, since neither Dedekind nor Hilbert meant to invoke the picture of clock arithmetic. (And Hilbert does not even mention anything as simple as n\mathbb{Z}_n).

    Now I don’t have Dedekind’s original text. Because also “Ordnung” is ambiguous. One meaning is “order” as in “ordered set”. But it also is used in the sense of “a collection of beings of the same nature” in the sense used as a taxonomic rank.

    Dedekind can’t have meant “ordered set”. So he must have meant “taxonomical order”. Maybe thinking of a “taxonomy of numbers”? I don’t don’t know.

    But anyway, I suppose that Hilbert’s “ring” is therefore also to be read as meaning “collection of beings”, as in “drug-dealer ring”. :-)

    Which, I must say, is too bad.

    • CommentRowNumber4.
    • CommentAuthorzskoda
    • CommentTimeSep 5th 2012

    What is the Dedekind’s original text ?

    • CommentRowNumber5.
    • CommentAuthorUrs
    • CommentTimeSep 5th 2012

    I don’t know, I just meant to say that I haven’t seen any original text on Dedekind’s “Ordnungen”. Maybe he didn’t even write it up. He is just being credited for the idea (by Hilbert).

    I have made further notes at ring - References - History

    • CommentRowNumber6.
    • CommentAuthorTim_Porter
    • CommentTimeSep 5th 2012
    • (edited Sep 5th 2012)

    A google search did turn up this, but that does not seem to answer the question.

    • CommentRowNumber7.
    • CommentAuthorUrs
    • CommentTimeSep 5th 2012

    A google search did turn up this,

    Yes, that’s already linked to in the entry.

    but that does not seem to answer the question.

    I believe I just answered the question in #3. :-)

    • CommentRowNumber8.
    • CommentAuthorUrs
    • CommentTimeSep 5th 2012
    • (edited Sep 5th 2012)

    By the way, I had put some text into the Idea-section. Not meant to be perfect. Please edit as you see the need.

    • CommentRowNumber9.
    • CommentAuthorTim_Porter
    • CommentTimeSep 5th 2012

    There is an Stackexchange question here, with another historical reference.

    • CommentRowNumber10.
    • CommentAuthorUrs
    • CommentTimeSep 5th 2012
    • (edited Sep 5th 2012)

    Started at ring an Examples-section. Just some very basic examples so far

    • CommentRowNumber11.
    • CommentAuthorzskoda
    • CommentTimeOct 2nd 2012
    • (edited Oct 2nd 2012)

    I added the following standard observation

    The structure of an AA opA\otimes A^{op}-ring (R,μ R,η)(R,\mu_R,\eta) is determined by the structure of AA as a ring, together with the two natural homomorphisms of rings s=η(1 A):ARs = \eta(-\otimes 1_A):A\to R and t=η(1 A):A opRt=\eta(1_A\otimes -):A^{op}\to R which have commuting images (s(a)t(a)=t(a)s(a)s(a)t(a')=t(a')s(a), for all a,aAa,a'\in A).

    This is very interesting when dualizing the notion of groupoid (algebra of functions/space duality) – source and target map in algebraic language get sometimes conveniently packed into AA opA\otimes A^{op}-ring language, as in the case of bialgebroids.

    • CommentRowNumber12.
    • CommentAuthorUrs
    • CommentTimeOct 2nd 2012
    • (edited Oct 2nd 2012)

    You should put something around that paragraph, wrapping it, something that allows to discern it as a new idea within the text that surropunds it. At least maybe a remark-environment.

    I knew it had to be there, but even so I only found it after hitting see changes.

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