Type errors

      <xsl:stylesheet
                  xmlns:sch="http://www.w3.org/2001/XMLSchema"
                  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                  version="2.0"
                  exclude-result-prefixes=" sch">
            <xsl:output  method="xml"
                        indent="yes"
                        omit-xml-declaration="yes"/>

            <xsl:template  match="/aaa">
                  <xsl:apply-templates  select="(1,2,3)"/>
                  <xsl:value-of  select="'a' + 'b'"/>
                  <xsl:variable  name="a"
                              select="2.34"
                              as="sch:integer"/>
                  <xsl:value-of  select="$a"/>
            </xsl:template>

      </xsl:stylesheet>

      <aaa/>

Error: