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https://en.wikipedia.org/wiki/Koan

Kōan (公案) (/ˈkæn, -ɑːn/; Chinese: 公案; pinyin: gōng'àn, [kʊ́ŋ ân]; Korean: 공안 gong-an; Vietnamese: công án) is a story, dialogue, question, or statement which is used in Zen practice to provoke the "great doubt" and to practice or test a student's progress in Zen.

Etymology