<p>In the paper, we revisit several approaches to the concept of uniform completion <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(X^{\textrm{ru}}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>X</mi> <mtext>ru</mtext> </msup> </math></EquationSource> </InlineEquation> of a vector lattice&#xa0;<i>X</i>. We show that many of these approaches yield the same result. In particular, if <i>X</i> is a sublattice of a uniformly complete vector lattice <i>Z</i> then <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(X^{\textrm{ru}}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>X</mi> <mtext>ru</mtext> </msup> </math></EquationSource> </InlineEquation> may be viewed as the intersection of all uniformly complete sublattices of <i>Z</i> containing&#xa0;<i>X</i>. <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(X^{\textrm{ru}}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>X</mi> <mtext>ru</mtext> </msup> </math></EquationSource> </InlineEquation> may also be constructed via a transfinite process of taking uniform adherences in <i>Z</i> with regulators coming from the previous adherences. If, in addition, <i>X</i> is majorizing in <i>Z</i> then <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(X^{\textrm{ru}}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>X</mi> <mtext>ru</mtext> </msup> </math></EquationSource> </InlineEquation> may be viewed as the uniform closure of <i>X</i> in&#xa0;<i>Z</i>. We show that <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(X^{\textrm{ru}}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>X</mi> <mtext>ru</mtext> </msup> </math></EquationSource> </InlineEquation> may also be characterized via a universal property: every positive operator from <i>X</i> to a uniformly complete vector lattice extends uniquely to&#xa0;<InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(X^{\textrm{ru}}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>X</mi> <mtext>ru</mtext> </msup> </math></EquationSource> </InlineEquation>. Moreover, the class of positive operators here may be replaced with several other important classes of operators (e.g., lattice homomorphisms). We also discuss conditions when the uniform adherence of a sublattice equals its uniform closure, and present an example (based on a construction by R.N.&#xa0;Ball and A.W.&#xa0;Hager) where this fails.</p>

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Relative uniform completion of a vector lattice

  • Eugene Bilokopytov,
  • Vladimir G. Troitsky

摘要

In the paper, we revisit several approaches to the concept of uniform completion \(X^{\textrm{ru}}\) X ru of a vector lattice X. We show that many of these approaches yield the same result. In particular, if X is a sublattice of a uniformly complete vector lattice Z then \(X^{\textrm{ru}}\) X ru may be viewed as the intersection of all uniformly complete sublattices of Z containing X. \(X^{\textrm{ru}}\) X ru may also be constructed via a transfinite process of taking uniform adherences in Z with regulators coming from the previous adherences. If, in addition, X is majorizing in Z then \(X^{\textrm{ru}}\) X ru may be viewed as the uniform closure of X in Z. We show that \(X^{\textrm{ru}}\) X ru may also be characterized via a universal property: every positive operator from X to a uniformly complete vector lattice extends uniquely to  \(X^{\textrm{ru}}\) X ru . Moreover, the class of positive operators here may be replaced with several other important classes of operators (e.g., lattice homomorphisms). We also discuss conditions when the uniform adherence of a sublattice equals its uniform closure, and present an example (based on a construction by R.N. Ball and A.W. Hager) where this fails.