How do kōans work?

> A kōan (公案?) (/ˈkoʊ.ɑːn/; Chinese: 公案; pinyin: gōng'àn; Korean: 공안 (kong'an); Vietnamese: công án) is a ***story, dialogue, question, or statement,*** (1) which is used in Zen practice to ***provoke the "great doubt"*** (2) and ***test a student's progress*** (3) in Zen practice. (4) Kōan Wikipedia 1. What are these stories, dialogues, questions, or statements? Where do they come from? How are they formulated? 2. What is "great doubt"? What is the goal of provoking "great doubt"? 3. What is being tested? What are the possible responses? How does the response quantify progress? 4. What is the overall goal of kōans? Perhaps considering a few kōans it is possible to illustrate the process from choosing or formulating the story, question, statement, or dialog, inspiring "great doubt", and how this measures progress and ultimately relates to the goal kōans / "great doubt" is supposed to achieve. Looking for an explanation based on any tradition using kōans including but not limited to [tag:zen] or [tag:mahayana]. Objective is to better understand the following content .