doesn't work because of the white space. This

  not(normalize-space(.) = preceding-sibling::bar)

  doesn't work because it only normalizes the context node, and this

  not(normalize-space(. )= normalize-space(preceding-sibling::bar))

but 
preceding-sibling::bar[normalize-space(.) = normalize-space(current())]
works or give  the system a bit of optimisation help and
<xsl:variable name="x" select="normalize-space(. )"/>
<xsl:if test="preceding-sibling::bar[normalize-space(.) = $x]">

but keys are likely to be more efficient I would expect,

David

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