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<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://htaiken.org/%E8%A4%87%E6%95%B0%E3%83%BB%E4%B9%B1%E4%BA%A4%E3%81%A7%E3%81%AEh%E4%BD%93%E9%A8%93%E8%AB%87/post-7318.html>