These sites should help you if you need to configure your apache (with an .htaccess file or directly in the Apache vhosts (VirtualHosts) config to redirect from non-www to www or the other way round so your site is SEO-compliant. They also describe cases for http vs. https.
www.seobook.com/archives/001714.shtml
www.remichael.de/tmp/lang/en/seo/redirect-domain-to-www-but-exclu...ubdomains/
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