this is my xml site map can any body say what is error?
<?xml version="1.0" encoding="UTF-8"?><?xml-stylesheet type="text/xsl" href="//dumlr.com/main-sitemap.xsl"?>
<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
<sitemap>
<loc>http://dumlr.com/post-sitemap.xml</loc>
<lastmod>2016-05-20T20:35:36+00:00</lastmod>
</sitemap>
<sitemap>
<loc>http://dumlr.com/page-sitemap.xml</loc>
<lastmod>2016-05-19T12:23:17+00:00</lastmod>
</sitemap>
<sitemap>
<loc>http://dumlr.com/category-sitemap.xml</loc>
<lastmod>2016-05-20T20:35:36+00:00</lastmod>
</sitemap>
<sitemap>
<loc>http://dumlr.com/author-sitemap.xml</loc>
<lastmod>2016-05-15T16:30:23+00:00</lastmod>
</sitemap>
</sitemapindex>
<!-- XML Sitemap generated by Yoast SEO -->