- Definition note (Σημείωση ορισμού)
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https://op.europa.eu/el/web/eu-vocabularies/concept/-/resource?uri=http://eurovoc.europa.eu/2855
https://metadata.un.org/thesaurus/1005230?lang=en
https://vocabularies.unesco.org/browser/thesaurus/en/page/?uri=http://vocabularies.unesco.org/thesaurus/concept252
https://www.wikidata.org/wiki/Q7867