December 6, 2012 10:1 WSPC/S0219-4988 171-JAA 1250139 Journal of Algebra and Its Applications Vol. 12, No. 1 (2013) 1250139 (16 pages) c World Scientific Publishing Company DOI: 10.1142/S0219498812501393 DEDEKIND COMPLETIONS OF BOUNDED ARCHIMEDEAN -ALGEBRAS GURAM BEZHANISHVILI∗, PATRICK J. MORANDI† and BRUCE OLBERDING‡ Department of Mathematical Sciences New Mexico State University Las Cruces, NM 88003-8001, USA ∗
[email protected] †
[email protected] ‡
[email protected] Received 19 July 2011 Accepted 28 February 2012 Published 10 December 2012 Communicated by D. Mundici All algebras considered in this paper are commutative with 1. Let ba be the category of bounded Archimedean -algebras. We investigate Dedekind completions and Dedekind complete algebras in ba . We give several characterizations for A ∈ ba to be Dedekind complete. Also, given A, B ∈ ba , we give several characterizations for B to be the Dedekind completion of A. We prove that unlike general Gelfand-Neumark-Stone duality, the duality for Dedekind complete algebras does not require any form of the Stone– Weierstrass Theorem. We show that taking the Dedekind completion is not functorial, but that it is functorial if we restrict our attention to those A ∈ ba that are Baer rings. As a consequence of our results, we give a new characterization of when A ∈ ba is a C∗-algebra. We also show that A is a C∗-algebra if and only if A is the inverse limit of an inverse family of clean C∗-algebras. We conclude the paper by discussing how to derive Gleason’s theorem about projective compact Hausdorff spaces and projective covers of compact Hausdorff spaces from our results.