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Semilattices which must contain a copy of \(2^ N\). (English) Zbl 0564.06003

The purpose of this note is to prove that certain semilattices must contain a copy of \(2^ N\). We show that any locally compact non-Lawson semilattice must contain such a subsemilattice. This result has interesting ramifications in several areas. For example, it is well known that any locally compact semilattice of finite breadth is Lawson. Finite breadth is generalized by J. Liukkonen and M. Mislove [Lect. Notes Math. 998, 202-214 (1983; Zbl 0516.43001)] to the notion of compactly finite breadth, whereby the locally compact semilattice S has compactly finite breadth if every compact subset X of S has a finite subset \(F\subset X\) with inf F\(=\inf X\). Our result shows that any semilattice satisfying this condition must be Lawson. This completes the work in [loc. cit.] by showing that a locally compact semilattice S has compactly finite breadth if and only if every complex homomorphism of the measure algebra M(S) is given by integration against a universally measurable semicharacter of S.

MSC:

06A12 Semilattices
22A26 Topological semilattices, lattices and applications
43A10 Measure algebras on groups, semigroups, etc.

Citations:

Zbl 0516.43001

References:

[1] Baartz, A.,The measure algebra of a locally compact semigroup, Pacific J. Math. 21 (1967), 199–214. · Zbl 0152.13304
[2] Gierz, G., et al.,A Compendium of Continuous Lattices, Springer-Verlag, Berlin, Heidelberg, New York (1980). · Zbl 0452.06001
[3] Gierz, G., J. Lawson and M. Mislove,A result about O(X), SCS Memo 5-19-1978.
[4] Lawson, J.,Algebraic conditions leading to continuous lattices, Proc. Amer. Math. Soc. 78 (1980), 477–481. · Zbl 0448.06006 · doi:10.1090/S0002-9939-1980-0556616-2
[5] Liukkonen, J. and M. Mislove,Measure algebras of semilattices, in: Lecture Notes in Math. 998, (1984), 202–214.
[6] Newman, S. E.,Measure algebras on idempotent semigroups, Pacific J. Math. 31 (1969), 161–169. · Zbl 0183.14701
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