<xsl:variable name="base_RDF_URI" select="'helm:rdf:www.cs.unibo.it/helm/rdf/backward//'"/>
<xsl:variable name="link_direction" select="' [dir=back]'"/>
<xsl:variable name="base_RDF_URI" select="'helm:rdf:www.cs.unibo.it/helm/rdf/backward//'"/>
<xsl:variable name="link_direction" select="' [dir=back]'"/>