why is declare invisible? how to say "Let X be ..."?

I'm working on formalizing the definitions in the SPARQL
spec[1], and since my larch tools[2] are getting crufty and
I just saw a bunch of nifty MathML products at XML 2004,
I'm trying to use MathML. I'm copying from the nifty
MathML test materials
  http://www.w3.org/Math/testsuite/static_toc.html
and using the stylesheet there
  http://www.w3.org/Math/testsuite/style/mathml.xsl
which seems to work pretty well in Mozilla firefox.

My work-in-progress is
  http://www.w3.org/2001/sw/DataAccess/mathml-rules.xml

For example, I encoded

  The set of RDF Terms, RDF-T, is RDF-U union RDF-L union RDF-B.

as

  <math xmlns="http://www.w3.org/1998/Math/MathML"> 
    <declare type="set">
      <ci> RDF_T </ci>
      <apply> 
	<union/> 
	<ci> RDF_U </ci> 
	<ci> RDF_L </ci> 
	<ci> RDF_B </ci> 
      </apply> 
    </declare>
  </math>

expecting to get something like

	RDF_T ::= RDF_U \U RDF_L \U RDF_B.

but the test materials say:

"Description:
          	declare test (no visible rendering)"
  --
http://www.w3.org/Math/testsuite/testsuite/Content/BasicContentElements/declare/rec-declare3.xml


Am I just using the wrong stylesheet to lay out my MatML?
Or is there some other preferred mathml syntax for "Let X be..."?


[1] http://www.w3.org/2001/sw/DataAccess/rq23/
[2] http://www.w3.org/XML/9711theory/#about-larch

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
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