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From Freudenthal’s spectral theorem to projectable hulls of unital Archimedean lattice-groups, through compactifications of minimal spectra

  • Richard N. Ball , Vincenzo Marra EMAIL logo , Daniel McNeill and Andrea Pedrini
From the journal Forum Mathematicum

Abstract

We use a landmark result in the theory of Riesz spaces – Freudenthal’s 1936 spectral theorem – to canonically represent any Archimedean lattice-ordered group G with a strong unit as a (non-separating) lattice-group of real-valued continuous functions on an appropriate G-indexed zero-dimensional compactification wGZG of its space ZG of minimal prime ideals. The two further ingredients needed to establish this representation are the Yosida representation of G on its space XG of maximal ideals, and the well-known continuous surjection of ZG onto XG. We then establish our main result by showing that the inclusion-minimal extension of this representation of G that separates the points of ZG – namely, the sublattice subgroup of C(ZG) generated by the image of G along with all characteristic functions of clopen (closed and open) subsets of ZG which are determined by elements of G – is precisely the classical projectable hull of G. Our main result thus reveals a fundamental relationship between projectable hulls and minimal spectra, and provides the most direct and explicit construction of projectable hulls to date. Our techniques do require the presence of a strong unit.

MSC 2010: 06F20; 54D35

Communicated by Manfred Droste


Award Identifier / Grant number: RBFR10DGUA

Funding statement: We gratefully acknowledge partial support by the Italian FIRB “Futuro in Ricerca” grant no. RBFR10DGUA, awarded by the Ministero dell’Istruzione, dell’Università e della Ricerca. The grant partially supported a visit of R. N. Ball to the Università degli Studi di Milano, Italy, during which the fundamental ideas of the present paper were developed.

Acknowledgements

We would like to express our thanks to an anonymous referee for detecting a serious blunder in an earlier version of this paper, and for providing us with Example 6.2. The same referee pointed out to us the relevance of [21] and [15] for our results (cf. Remark 6.3). Further comments by the referee led us to improve the presentation of our results. Finally, we are grateful to S. J. van Gool for pointing out to us that the use of the standard extension result [1, Section V.4, Lemma 1] could shorten the proof of Theorem 5.1.

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Received: 2017-3-2
Published Online: 2017-8-12
Published in Print: 2018-3-1

© 2018 Walter de Gruyter GmbH, Berlin/Boston

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