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    • CommentRowNumber1.
    • CommentAuthorUrs
    • CommentTimeApr 13th 2019

    some minimum, for cross-linking with Sp(n).Sp(1)

    v1, current

    • CommentRowNumber2.
    • CommentAuthorUrs
    • CommentTimeApr 13th 2019

    changed page name to singular

    v1, current

    • CommentRowNumber3.
    • CommentAuthorUrs
    • CommentTimeMay 16th 2019
    • (edited May 16th 2019)

    When I started this entry, I deliberately changed the wording of the definition as compared to what one finds in most of the literature.

    I have added now a remark on this point, for clarity:

    Beware that most texts insists on stating the choices in the definition of the central product as that of

    Beware that most texts insists on stating the choices in Def. \ref{CentralProduct} as that of

    1. two separate subgroups C iι iZ(G i)C_i \xhookrightarrow{\iota_i} Z(G_i)

    2. an isomorphism C 1ϕC 2C_1 \xrightarrow[\simeq]{\phi} C_2 between them

    and insists that the second group acts via () 1ϕ(-)^{-1}\circ \phi.

    These clauses matter if one thinks of the subgroup inclusions as in material set theory. But we speak structural set theory, which means that a subgroup inclusion as in (eq:SubgroupInclusion) is really a choice of monic homomorphism, and this choice already absorbs the choice of ϕ\phi and or () 1ϕ(-)^{-1}\circ \phi above.

    diff, v4, current

    • CommentRowNumber4.
    • CommentAuthorUrs
    • CommentTimeNov 21st 2020

    added mentioning of the example of spin^c-groups

    diff, v5, current