Need help adding if / else statements in XSL markup

I need to add some if / else statements to an XSL file.  


I understand that I can do something like this:

    <xsl:for-each select="CATALOG/CD">
            <xsl:if match=".[TOPIC='topic1']">
              <tr>
          <td><xsl:value-of select="TITLE"/></td>
          <td><xsl:value-of select="TOPIC"/></td>
        </tr>
        </xsl:if>
      </xsl:for-each>


However, .. how would I extend this to have mutiple conditionals, .. and with some "NOT EQUAL TO" operators?

if topic = "topic1" OR topic = "topic2" OR topic = "topic3"

if topic != "topic1" AND topic != "topic2" AND topic != "topic3"

Is this possible somehow?  If so, how?

Thanks!
- Yvan